diff --git a/src/openforms/submissions/cosigning.py b/src/openforms/submissions/cosigning.py
index c3bae8bd1a..f070253e59 100644
--- a/src/openforms/submissions/cosigning.py
+++ b/src/openforms/submissions/cosigning.py
@@ -87,6 +87,11 @@ def _find_component(self) -> Component | None:
         """
         Discover the Formio cosign component in the submission/form.
         """
+        from .form_logic import check_submission_logic
+        from .logic.datastructures import DataContainer
+
+        check_submission_logic(self.submission)
+
         # use the complete view on the Formio component tree(s)
         configuration_wrapper = self.submission.total_configuration_wrapper
 
@@ -94,6 +99,18 @@ def _find_component(self) -> Component | None:
         # component.
         for component in configuration_wrapper.component_map.values():
             if component["type"] == "cosign":
+                # we can't just blindly return the component, as it may be conditionally
+                # displayed, which is equivalent to "cosign not relevant". See
+                # https://github.com/open-formulieren/open-forms/issues/3901
+                container = DataContainer(
+                    self.submission.load_submission_value_variables_state()
+                )
+                visible = configuration_wrapper.is_visible_in_frontend(
+                    component["key"],
+                    values=container.data,
+                )
+                if not visible:
+                    return None
                 return component
         return None
 
diff --git a/src/openforms/submissions/tests/test_post_submission_event.py b/src/openforms/submissions/tests/test_post_submission_event.py
index bcbc50d8ad..bffe0ecab4 100644
--- a/src/openforms/submissions/tests/test_post_submission_event.py
+++ b/src/openforms/submissions/tests/test_post_submission_event.py
@@ -15,7 +15,8 @@
 from openforms.authentication.service import AuthAttribute
 from openforms.config.models import GlobalConfiguration
 from openforms.emails.tests.factories import ConfirmationEmailTemplateFactory
-from openforms.forms.tests.factories import FormDefinitionFactory
+from openforms.forms.constants import LogicActionTypes, PropertyTypes
+from openforms.forms.tests.factories import FormDefinitionFactory, FormLogicFactory
 from openforms.payments.constants import PaymentStatus
 from openforms.payments.tests.factories import SubmissionPaymentFactory
 from openforms.registrations.base import PreRegistrationResult
@@ -24,7 +25,7 @@
 )
 from openforms.utils.tests.logging import ensure_logger_level
 
-from ..constants import PostSubmissionEvents
+from ..constants import PostSubmissionEvents, RegistrationStatuses
 from ..models import SubmissionReport
 from ..tasks import on_post_submission_event
 from .factories import SubmissionFactory
@@ -996,6 +997,87 @@ def test_cosign_not_required_but_filled_in_does_not_proceed_with_registration(se
         self.assertTrue(submission.confirmation_email_sent)
         self.assertEqual(submission.auth_info.value, "111222333")
 
+    @tag("gh-3901", "hlmr-86")
+    def test_cosign_required_but_hidden_proceeds_with_registration(self):
+        """
+        A conditionally hidden cosign component may not block registration.
+        """
+        submission = SubmissionFactory.from_components(
+            components_list=[
+                {
+                    "key": "cosign",
+                    "type": "cosign",
+                    "label": "Cosign component",
+                    "validate": {"required": True},
+                    "hidden": True,
+                },
+            ],
+            submitted_data={"cosign": ""},
+            completed=True,
+            cosign_complete=False,
+            form__registration_backend="email",
+            form__registration_backend_options={"to_emails": ["test@registration.nl"]},
+            auth_info__attribute=AuthAttribute.bsn,
+            auth_info__value="111222333",
+            language_code="en",
+        )
+        assert submission.registration_status == RegistrationStatuses.pending
+
+        on_post_submission_event(submission.pk, PostSubmissionEvents.on_completion)
+
+        submission.refresh_from_db()
+        self.assertEqual(submission.registration_status, RegistrationStatuses.success)
+
+    @tag("gh-3901", "hlmr-86")
+    def test_cosign_required_and_visible_via_logic_does_not_proceed_with_registration(
+        self,
+    ):
+        """
+        A conditionally displayed cosign component must block registration.
+        """
+        submission = SubmissionFactory.from_components(
+            components_list=[
+                {
+                    "key": "cosign",
+                    "type": "cosign",
+                    "label": "Cosign component",
+                    "validate": {"required": True},
+                    "hidden": True,
+                },
+            ],
+            submitted_data={"cosign": ""},
+            completed=True,
+            cosign_complete=False,
+            form__registration_backend="email",
+            form__registration_backend_options={"to_emails": ["test@registration.nl"]},
+            auth_info__attribute=AuthAttribute.bsn,
+            auth_info__value="111222333",
+            language_code="en",
+        )
+        FormLogicFactory.create(
+            form=submission.form,
+            json_logic_trigger=True,
+            actions=[
+                {
+                    "action": {
+                        "type": LogicActionTypes.property,
+                        "property": {
+                            "type": PropertyTypes.bool,
+                            "value": "hidden",
+                        },
+                        "state": False,
+                    },
+                    "component": "cosign",
+                }
+            ],
+        )
+        assert submission.registration_status == RegistrationStatuses.pending
+
+        on_post_submission_event(submission.pk, PostSubmissionEvents.on_completion)
+
+        submission.refresh_from_db()
+        self.assertEqual(submission.registration_status, RegistrationStatuses.pending)
+
     @tag("gh-3924")
     def test_payment_complete_does_not_set_retry_flag(self):
         submission = SubmissionFactory.create(