diff --git a/src/App.jsx b/src/App.jsx
index 12067c7..7feb932 100644
--- a/src/App.jsx
+++ b/src/App.jsx
@@ -935,7 +935,7 @@ export default function App({ edpFetch }) {
                 subjectDatas[periodCode][subjectCode].push({ value: newGrade.value, coef: newGrade.coef, scale: newGrade.scale, isSignificant: newGrade.isSignificant, classAverage: newGrade.classAverage });
                 const nbSubjectGrades = periods[periodCode].subjects[subjectCode]?.grades.filter((el) => el.isSignificant).length ?? 0;
                 const subjectAverage = periods[periodCode].subjects[subjectCode].average;
-                const oldGeneralAverage = isNaN(periods[periodCode].generalAverage) ? 10 : periods[periodCode].generalAverage;
+                const oldGeneralAverage = isNaN(periods[periodCode]?.generalAverage) ? 10 : periods[periodCode]?.generalAverage;
                 const average = calcAverage(subjectDatas[periodCode][subjectCode]);
                 const classAverage = calcClassAverage(subjectDatas[periodCode][subjectCode]);
 
diff --git a/src/components/app/Account/Account.jsx b/src/components/app/Account/Account.jsx
index 8cad48c..053beee 100644
--- a/src/components/app/Account/Account.jsx
+++ b/src/components/app/Account/Account.jsx
@@ -244,7 +244,7 @@ export default function Account({ schoolLife, fetchSchoolLife, fetchAdministrati
                                             )}
                                             {module?.params?.DocumentsAdministratifActif === "1" && documents?.administratifs?.length > 0 && (
                                                 <div className="document-category">
-                                                    <h3>Documents Administratifs</h3>
+                                                    <h3>Documents administratifs</h3>
                                                     {documents.administratifs.map(file => (
                                                         <div className="file-box">
                                                             <FileComponent key={file.id} file={file} />
@@ -266,7 +266,7 @@ export default function Account({ schoolLife, fetchSchoolLife, fetchAdministrati
                                             )}
                                             {module?.params?.DocumentsVSActif === "1" && documents?.viescolaire?.length > 0 && (
                                                 <div className="document-category">
-                                                    <h3>Vie Scolaire</h3>
+                                                    <h3>Vie scolaire</h3>
                                                     {documents.viescolaire.map(file => (
                                                         <div className="file-box">
                                                             <FileComponent key={file.id} file={file} />
@@ -277,7 +277,7 @@ export default function Account({ schoolLife, fetchSchoolLife, fetchAdministrati
                                             )}
                                             {module?.params?.DocumentsEntrepriseActif === "1" && documents?.entreprises?.length > 0 && (
                                                 <div className="document-category">
-                                                    <h3>Documents Entreprise</h3>
+                                                    <h3>Documents entreprise</h3>
                                                     {documents.entreprises.map(file => (
                                                         <div className="file-box">
                                                             <FileComponent key={file.id} file={file} />
diff --git a/src/components/app/Grades/MobileResults.jsx b/src/components/app/Grades/MobileResults.jsx
index 0772fa1..47333f4 100644
--- a/src/components/app/Grades/MobileResults.jsx
+++ b/src/components/app/Grades/MobileResults.jsx
@@ -110,7 +110,7 @@ export default function Results({ activeAccount, sortedGrades, selectedPeriod, s
                                     <TooltipTrigger>
                                         <span>
                                             {sortedGrades && sortedGrades[selectedPeriod]
-                                                ? <Grade grade={{ value: sortedGrades[selectedPeriod].generalAverage ?? "N/A", scale: 20, coef: 1, isSignificant: true }} />
+                                                ? <Grade grade={{ value: sortedGrades[selectedPeriod]?.generalAverage ?? "N/A", scale: 20, coef: 1, isSignificant: true }} />
                                                 : <ContentLoader
                                                     animate={settings.get("displayMode") === "quality"}
                                                     speed={1}
@@ -139,7 +139,7 @@ export default function Results({ activeAccount, sortedGrades, selectedPeriod, s
                                     </TooltipContent>
                                 </Tooltip>
                                 : sortedGrades && sortedGrades[selectedPeriod]
-                                    ? <Grade grade={{ value: sortedGrades[selectedPeriod].generalAverage ?? "-", scale: 20, coef: 1, isSignificant: true }} />
+                                    ? <Grade grade={{ value: sortedGrades[selectedPeriod]?.generalAverage ?? "-", scale: 20, coef: 1, isSignificant: true }} />
                                     : <ContentLoader
                                         animate={settings.get("displayMode") === "quality"}
                                         speed={1}
diff --git a/src/components/app/Grades/Results.jsx b/src/components/app/Grades/Results.jsx
index da6a536..512549e 100644
--- a/src/components/app/Grades/Results.jsx
+++ b/src/components/app/Grades/Results.jsx
@@ -113,7 +113,7 @@ export default function Results({ activeAccount, sortedGrades, selectedPeriod, s
                                     <TooltipTrigger>
                                         <span>
                                             {sortedGrades && sortedGrades[selectedPeriod]
-                                                ? <Grade grade={{ value: sortedGrades[selectedPeriod].generalAverage ?? "N/A", scale: 20, coef: 1, isSignificant: true }} />
+                                                ? <Grade grade={{ value: sortedGrades[selectedPeriod]?.generalAverage ?? "N/A", scale: 20, coef: 1, isSignificant: true }} />
                                                 : <ContentLoader
                                                     animate={settings.get("displayMode") === "quality"}
                                                     speed={1}
@@ -142,7 +142,7 @@ export default function Results({ activeAccount, sortedGrades, selectedPeriod, s
                                     </TooltipContent>
                                 </Tooltip>
                                 : sortedGrades && sortedGrades[selectedPeriod]
-                                    ? <Grade grade={{ value: sortedGrades[selectedPeriod].generalAverage ?? "-", scale: 20, coef: 1, isSignificant: true }} />
+                                    ? <Grade grade={{ value: sortedGrades[selectedPeriod]?.generalAverage ?? "-", scale: 20, coef: 1, isSignificant: true }} />
                                     : <ContentLoader
                                         animate={settings.get("displayMode") === "quality"}
                                         speed={1}
diff --git a/src/components/app/Homeworks/Calendar.jsx b/src/components/app/Homeworks/Calendar.jsx
index 9a80efd..ff737e6 100644
--- a/src/components/app/Homeworks/Calendar.jsx
+++ b/src/components/app/Homeworks/Calendar.jsx
@@ -7,6 +7,7 @@ import { fr } from 'date-fns/locale';
 import DropDownArrow from "../../graphics/DropDownArrow";
 
 import './Calendar.css';
+import { isValidDateFormat } from '../../../utils/date';
 
 export default function Calendar({ onDateClick }) {
     const today = new Date()
@@ -20,7 +21,7 @@ export default function Calendar({ onDateClick }) {
 
     const navigate = useNavigate();
     const hashParameters = location.hash.split(";");
-    const selectedISODate = hashParameters[0].slice(1) || format(today, "yyyy-MM-dd");
+    const selectedISODate = isValidDateFormat(hashParameters[0].slice(1)) ? hashParameters[0].slice(1) : Date.now();
     const selectedDate = new Date(selectedISODate);
 
     const userHomeworks = useUserData("sortedHomeworks");
diff --git a/src/components/app/Homeworks/Interrogation.jsx b/src/components/app/Homeworks/Interrogation.jsx
index 32edd0b..778cce0 100644
--- a/src/components/app/Homeworks/Interrogation.jsx
+++ b/src/components/app/Homeworks/Interrogation.jsx
@@ -62,14 +62,14 @@ export default function Interrogation({ task }) { // This component only exists
     const taskColor = typeof task.id === "number" ? textToHSL(task.subjectCode) : undefined;
 
     return typeof task.id === "number"
-        ? <div tabIndex="0" role="a" onKeyDown={(e) => handleKeyDown(e, task.date, task.id)} onClick={() => handleClick(task.date, task.id)} className={`upcoming-assignments ${currentSortedHomeworks[task.date][task.index].isDone ? "done" : ""}`}
+        ? <div tabIndex="0" role="a" onKeyDown={(e) => handleKeyDown(e, task.date, task.id)} onClick={() => handleClick(task.date, task.id)} className={`upcoming-assignments ${currentSortedHomeworks[task.date][task.index]?.isDone ? "done" : ""}`}
             style={{
                 "--subject-main-color": actualDisplayTheme === "dark" ? `hsl(${taskColor[0]}, ${taskColor[1]}%, ${taskColor[2]}%)` : `hsl(${taskColor[0]}, ${taskColor[1] - 20}%, ${taskColor[2] - 30}%)`,
                 "--subject-bg-color": actualDisplayTheme === "dark" ? `hsla(${taskColor[0]}, ${taskColor[1]}%, ${taskColor[2]}%, .2)` : `hsla(${taskColor[0]}, ${taskColor[1] - 20}%, ${taskColor[2] - 30}%, .2)`,
                 // "--text-color-task": `hsl(${taskColor[0]}, ${taskColor[1] - 20}%, ${taskColor[2] - 20}%)`,
                 // "--background-color-task": `hsl(${taskColor[0]}, ${taskColor[1] - 5}%, ${taskColor[2] - 5}%)`,
             }}>
-            <CheckBox onChange={() => { checkTask(task.date, task.index) }} ref={taskCheckboxRef} checked={currentSortedHomeworks[task.date][task.index].isDone} id={`${task.id}-upcoming-assignments"`} onMouseEnter={() => isMouseInCheckBoxRef.current = true} onMouseLeave={() => isMouseInCheckBoxRef.current = false} style={{ "backgroundImage": currentSortedHomeworks[task.date][task.index].isDone ? `url("data:image/svg+xml,%3Csvg width='126' height='90' viewBox='0 0 126 90' fill='none' xmlns='http://www.w3.org/2000/svg'%3E%3Cpath d='M3.00999 29.4982L4.7539 27.7442C8.77118 23.7036 15.3475 23.8312 19.205 28.0246L47.306 58.5723C48.849 60.2496 51.4795 60.3007 53.0864 58.6844L108.318 3.13256C112.228 -0.799963 118.591 -0.799963 122.501 3.13256L122.99 3.62419C126.868 7.5247 126.868 13.8249 122.99 17.7254L52.9741 88.147C51.4102 89.72 48.8649 89.72 47.301 88.147L3.00999 43.5994C-0.868052 39.6989 -0.868055 33.3987 3.00999 29.4982Z' fill='hsl(${taskColor[0]}, ${taskColor[1]}%, ${taskColor[2]}%)'/%3E%3C/svg%3E")` : "" }} />
+            <CheckBox onChange={() => { checkTask(task.date, task.index) }} ref={taskCheckboxRef} checked={currentSortedHomeworks[task.date][task.index]?.isDone} id={`${task.id}-upcoming-assignments"`} onMouseEnter={() => isMouseInCheckBoxRef.current = true} onMouseLeave={() => isMouseInCheckBoxRef.current = false} style={{ "backgroundImage": currentSortedHomeworks[task.date][task.index]?.isDone ? `url("data:image/svg+xml,%3Csvg width='126' height='90' viewBox='0 0 126 90' fill='none' xmlns='http://www.w3.org/2000/svg'%3E%3Cpath d='M3.00999 29.4982L4.7539 27.7442C8.77118 23.7036 15.3475 23.8312 19.205 28.0246L47.306 58.5723C48.849 60.2496 51.4795 60.3007 53.0864 58.6844L108.318 3.13256C112.228 -0.799963 118.591 -0.799963 122.501 3.13256L122.99 3.62419C126.868 7.5247 126.868 13.8249 122.99 17.7254L52.9741 88.147C51.4102 89.72 48.8649 89.72 47.301 88.147L3.00999 43.5994C-0.868052 39.6989 -0.868055 33.3987 3.00999 29.4982Z' fill='hsl(${taskColor[0]}, ${taskColor[1]}%, ${taskColor[2]}%)'/%3E%3C/svg%3E")` : "" }} />
             <span><span className="interrogation-label">{task.subject}</span></span>
             <span>{formatDateRelative(new Date(task.date))}</span>
         </div>
diff --git a/src/utils/date.js b/src/utils/date.js
index d2477f1..7416823 100644
--- a/src/utils/date.js
+++ b/src/utils/date.js
@@ -29,6 +29,14 @@ export function formatDateRelative(date, short=true) {
     }
 }
 
+export function isValidDateFormat(dateString) {
+    if (!dateString) {
+        return false;
+    }
+    const regex = /^\d{4}-\d{2}-\d{2}$/; // Matches YYYY-MM-DD format
+    return regex.test(dateString);
+}
+
 export function getCurrentSchoolYear() {
     /**
      * return an array: