diff --git a/src/app/widgets/NavbarConnection/FirmwareSelector.jsx b/src/app/widgets/NavbarConnection/FirmwareSelector.jsx
index 4a42c03bb..b3b70e61d 100644
--- a/src/app/widgets/NavbarConnection/FirmwareSelector.jsx
+++ b/src/app/widgets/NavbarConnection/FirmwareSelector.jsx
@@ -24,9 +24,11 @@
 import React from 'react';
 import cx from 'classnames';
 import { uniqueId } from 'lodash';
+import { GRBL } from 'app/constants';
 import styles from './Index.styl';
 
 const FirmwareSelector = ({ options = [], selectedFirmware, handleSelect }) => {
+    selectedFirmware = selectedFirmware || GRBL; // null check
     return (
         <div className={styles.firmwareSelector}>
             <div className={styles.selectorWrapper}>
diff --git a/src/server/controllers/Grblhal/GrblHalController.js b/src/server/controllers/Grblhal/GrblHalController.js
index 76f5bab71..1869b5f04 100644
--- a/src/server/controllers/Grblhal/GrblHalController.js
+++ b/src/server/controllers/Grblhal/GrblHalController.js
@@ -679,7 +679,7 @@ class GrblHalController {
                     this.sender.unhold();
                 }
                 this.sender.ack();
-                this.sender.next();
+                this.sender.next({ isOk: true });
                 return;
             }
 
@@ -692,7 +692,7 @@ class GrblHalController {
                     log.debug(`Stop sending G-code: hold=${hold}, sent=${sent}, received=${received + 1}`);
                 }
                 this.sender.ack();
-                this.sender.next();
+                this.sender.next({ isOk: true });
                 return;
             }
 
@@ -1633,7 +1633,7 @@ class GrblHalController {
                 } else {
                     this.workflow.pause();
                     await delay(100);
-                    this.write('!');
+                    this.write(GRBLHAL_REALTIME_COMMANDS.FEED_HOLD);
                 }
             },
             'resume': () => {
@@ -1642,24 +1642,15 @@ class GrblHalController {
             },
             'gcode:resume': async () => {
                 log.debug('gcode:resume called - program to continue sending');
-                const [type] = args;
                 if (this.event.hasEnabledEvent(PROGRAM_RESUME)) {
                     this.feederCB = () => {
-                        if (type === GRBLHAL) {
-                            this.write(GRBLHAL_REALTIME_COMMANDS.CYCLE_START);
-                        } else {
-                            this.write('~');
-                        }
+                        this.write(GRBLHAL_REALTIME_COMMANDS.CYCLE_START);
                         this.workflow.resume();
                         this.feederCB = null;
                     };
                     this.event.trigger(PROGRAM_RESUME);
                 } else {
-                    if (type === GRBLHAL) {
-                        this.write(GRBLHAL_REALTIME_COMMANDS.CYCLE_START);
-                    } else {
-                        this.write('~');
-                    }
+                    this.write(GRBLHAL_REALTIME_COMMANDS.CYCLE_START);
                     await delay(1000);
                     this.workflow.resume();
                 }
diff --git a/src/server/lib/Sender.js b/src/server/lib/Sender.js
index 994d3b76a..21bbdeadd 100644
--- a/src/server/lib/Sender.js
+++ b/src/server/lib/Sender.js
@@ -85,8 +85,8 @@ class SPCharCounting {
         }
     }
 
-    process() {
-        this.callback && this.callback(this);
+    process(isOk) {
+        this.callback && this.callback(this, isOk);
     }
 
     reset() {
@@ -195,8 +195,8 @@ class Sender extends events.EventEmitter {
 
         // character-counting
         if (type === SP_TYPE_CHAR_COUNTING) {
-            this.sp = new SPCharCounting(options, (sp) => {
-                if (sp.queue.length > 0) {
+            this.sp = new SPCharCounting(options, (sp, isOk) => {
+                if (sp.queue.length > 0 && isOk) { // only remove line length from buffer if ok was sent
                     const lineLength = sp.queue.shift();
                     sp.dataLength -= lineLength;
                 }
@@ -410,7 +410,7 @@ class Sender extends events.EventEmitter {
     // Tells the sender to send more data.
     // @return {boolean} Returns true on success, false otherwise.
     next(options = {}) {
-        const { startFromLine, timePaused, forceEnd } = options;
+        const { startFromLine, timePaused, forceEnd, isOk } = options;
 
         if (!this.state.gcode) {
             return false;
@@ -451,7 +451,7 @@ class Sender extends events.EventEmitter {
         }
 
         if (this.sp) {
-            this.sp.process();
+            this.sp.process(isOk);
         }
 
         // Elapsed Time