Update:
I got a new exception. Tried to use Ctrl+Z to undo something after I got the error. After that the model closed and I got this in my MATLAB Command Window:
Warning: An error has occurred during refresh of Action named blockFitToContentAction.
Warning: Generator should return a DAStudio.ToolSchema.
Unhandled exception thrown during 'handleUndo' of command 'Parameter Changes'.
Assertion failed: cannot undoToChangeLevel within a transaction at B:\matlab\src\m3i\kernel\deviant\Deviant.cpp:47:
[ 0] 0x00007ff81f70a063 D:\Program Files\MATLAB\R2021a\bin\win64\libmwfl.dll+00041059 foundation::core::diag::thread_context::unspecified_bool+00000051
[ 1] 0x00007ff81f707338 D:\Program Files\MATLAB\R2021a\bin\win64\libmwfl.dll+00029496 foundation::core::diag::stacktrace_base::capture+00000024
[ 2] 0x00007fff5ef42b79 D:\Program Files\MATLAB\R2021a\bin\win64\m3i.dll+00994169 M3I::Exception::Exception+00000169
[ 3] 0x00007fff5ee6de0e D:\Program Files\MATLAB\R2021a\bin\win64\m3i.dll+00122382 mwboost::serialization::singleton_module::get_lock+00000270
[ 4] 0x00007fff5ef08551 D:\Program Files\MATLAB\R2021a\bin\win64\m3i.dll+00755025 M3I::Deviant::undoToChangeLevel+00000177
[ 5] 0x00007fff5ef08427 D:\Program Files\MATLAB\R2021a\bin\win64\m3i.dll+00754727 M3I::Deviant::undoGroup+00000359
[ 6] 0x00007fff3f89ea21 D:\Program Files\MATLAB\R2021a\bin\win64\glue2.dll+00911905 GLUE2::Command::handleUndoInternal+00001505
[ 7] 0x00007fff3fd69370 D:\Program Files\MATLAB\R2021a\bin\win64\glue2.dll+05935984 GLUE2::Util::BusyCursor::restoreCursor+00000064
[ 8] 0x00007fff3f89e357 D:\Program Files\MATLAB\R2021a\bin\win64\glue2.dll+00910167 GLUE2::Command::handleUndo+00000279
[ 9] 0x00007fffaec38707 D:\Program Files\MATLAB\R2021a\bin\win64\glee_util.dll+00427783 GLEE::Command::undo+00000343
[ 10] 0x00007fffaec3eb57 D:\Program Files\MATLAB\R2021a\bin\win64\glee_util.dll+00453463 GLEE::UndoRedoCommandTarget::clearUndoStackFromAndIncluding+00001879
[ 11] 0x00007fffaec3feef D:\Program Files\MATLAB\R2021a\bin\win64\glee_util.dll+00458479 GLEE::UndoRedoCommandTarget::undo+00000703
[ 12] 0x00007fff3f4c6346 D:\Program Files\MATLAB\R2021a\bin\win64\dastudio_platform.dll+00090950 PLATFORM::DomainImpl::undo+00000278
[ 13] 0x00007fff3f4fcbb0 D:\Program Files\MATLAB\R2021a\bin\win64\dastudio_platform.dll+00314288 PLATFORM::InterfaceManager::unregisterApplicationIM+00025120
[ 14] 0x00007fffcafb3a5e bin\win64\pgo\mcos_impl.dll+00342622
[ 15] 0x00007fffcafb3005 bin\win64\pgo\mcos_impl.dll+00339973
[ 16] 0x00007fffcafb2ca0 bin\win64\pgo\mcos_impl.dll+00339104
[ 17] 0x00007fffcaff7ab7 bin\win64\pgo\mcos_impl.dll+00621239 mdMethodListAllFcn+00065895
[ 18] 0x00007fffcb1ad400 bin\win64\pgo\mcos_impl.dll+02413568 mwboost::serialization::singleton_module::unlock+01172572
[ 19] 0x00007fffcb218bfc bin\win64\pgo\mcos_impl.dll+02853884 namedArgsToCell+00004800
[ 20] 0x00007fffcb225b9d bin\win64\pgo\mcos_impl.dll+02907037 namedArgsToCell+00057953
[ 21] 0x00007ff8130915d8 bin\win64\mcos.dll+00136664 omDirectCallMethod+00000072
[ 22] 0x00007fffeb7eb14f bin\win64\pgo\libmwlxeindexing.dll+00438607 MathWorks::lxe::MatrixModuleImplementation::SetHeterogeneousArray+00011335
[ 23] 0x00007fffeb86b8ab bin\win64\pgo\libmwlxeindexing.dll+00964779 MathWorks::lxe::intermediate_paren_ref_place+00006699
[ 24] 0x00007fffeb785cdf bin\win64\pgo\libmwlxeindexing.dll+00023775 MathWorks::lxe::MultiValue::SetCellArray+00000115
[ 25] 0x00007fffeb785cdf bin\win64\pgo\libmwlxeindexing.dll+00023775 MathWorks::lxe::MultiValue::SetCellArray+00000115
[ 26] 0x00007fffeb8093e2 bin\win64\pgo\libmwlxeindexing.dll+00562146 MathWorks::lxe::DereferenceRplaceToXvalueZeroOutputs+00000030
[ 27] 0x00007fffeb7d7c83 bin\win64\pgo\libmwlxeindexing.dll+00359555 MathWorks::lxe::at_rparen0+00000391
[ 28] 0x00007fffd302636f bin\win64\pgo\m_lxe.dll+00353135
[ 29] 0x00007fffd4cb7dd1 bin\win64\pgo\m_lxe.dll+30309841 mwboost::archive::detail::pointer_oserializer<mwboost::archive::binaryTerm_oarchive,MathWorks::lxe::MatlabIrTree>::save_object_ptr+00329281
[ 30] 0x00007fffd30423c7 bin\win64\pgo\m_lxe.dll+00467911 MathWorks::lxe::initializeFcn+00106135
[ 31] 0x00007fffd3041261 bin\win64\pgo\m_lxe.dll+00463457 MathWorks::lxe::initializeFcn+00101681
[ 32] 0x00007fffd3040c72 bin\win64\pgo\m_lxe.dll+00461938 MathWorks::lxe::initializeFcn+00100162
[ 33] 0x00007fffd30453f3 bin\win64\pgo\m_lxe.dll+00480243 MathWorks::lxe::initializeFcn+00118467
[ 34] 0x00007fffd304509f bin\win64\pgo\m_lxe.dll+00479391 MathWorks::lxe::initializeFcn+00117615
[ 35] 0x00007fffd302d2c0 bin\win64\pgo\m_lxe.dll+00381632 MathWorks::lxe::initializeFcn+00019856
[ 36] 0x00007fffd302c0eb bin\win64\pgo\m_lxe.dll+00377067 MathWorks::lxe::initializeFcn+00015291
[ 37] 0x00007fffd302b136 bin\win64\pgo\m_lxe.dll+00373046 MathWorks::lxe::initializeFcn+00011270
[ 38] 0x00007fffd3063a96 bin\win64\pgo\m_lxe.dll+00604822 MathWorks::lxe::initializeFcn+00243046
[ 39] 0x00007fffd306380a bin\win64\pgo\m_lxe.dll+00604170 MathWorks::lxe::initializeFcn+00242394
[ 40] 0x00007fffd3061993 bin\win64\pgo\m_lxe.dll+00596371 MathWorks::lxe::initializeFcn+00234595
[ 41] 0x00007ff8148ff68c bin\win64\pgo\libmx.dll+00652940 matrix::detail::noninlined::mx_array_api::mxFevalFunctionHandle+00000036
[ 42] 0x00007ffffe925a85 bin\win64\pgo\m_interpreter.dll+00154245 mwboost::serialization::singleton<mwboost::serialization::extended_type_info_typeid<MathWorks::ExecutionEvents::UncaughtErrorEvent> >::singleton<mwboost::serialization::extended_type_info_typeid<MathWorks::ExecutionEvents::UncaughtErrorEvent> >+00027445
[ 43] 0x00007ffffbc08bea D:\Program Files\MATLAB\R2021a\bin\win64\builtin.dll+00101354 MathWorks::builtin::BuiltinFcn::invoke+00001130
[ 44] 0x00007ff8107c4b9c bin\win64\pgo\m_dispatcher.dll+00150428 Mfh_MATLAB_fn_impl::dispatch_mf_with_reuse+00000136
[ 45] 0x00007ff8107b4630 bin\win64\pgo\m_dispatcher.dll+00083504 Mfh_MATLAB_fn_impl::ensure_loading_of_load_module+00001856
[ 46] 0x00007ff8107b47b9 bin\win64\pgo\m_dispatcher.dll+00083897 Mfh_MATLAB_fn_impl::dispatch_with_reuse+00000045
[ 47] 0x00007fffd3027e2e bin\win64\pgo\m_lxe.dll+00359982
[ 48] 0x00007fffd3023c2e bin\win64\pgo\m_lxe.dll+00343086
[ 49] 0x00007fffd3023b87 bin\win64\pgo\m_lxe.dll+00342919
[ 50] 0x00007ffffe90d550 bin\win64\pgo\m_interpreter.dll+00054608 inCallFcn+00000084
[ 51] 0x00007fffd318c76a bin\win64\pgo\m_lxe.dll+01820522 mwboost::archive::detail::oserializer<mwboost::archive::binaryTerm_oarchive,MathWorks::lxe::ClosedAbstractionFunctionDescriptorOwningIrTree>::oserializer<mwboost::archive::binaryTerm_oarchive,MathWorks::lxe::ClosedAbstractionFunctionDescriptorOwningIrTree>+00024646
[ 52] 0x00007ffffe9126e2 bin\win64\pgo\m_interpreter.dll+00075490 inCallFcnWithTrap+00000098
[ 53] 0x00007fff3d644bc9 D:\Program Files\MATLAB\R2021a\bin\win64\dig.dll+03623881 dig::FunctionInfoToArray+00000649
[ 54] 0x00007fff3d61121a D:\Program Files\MATLAB\R2021a\bin\win64\dig.dll+03412506 dig::ActionCallback::operator()+00000826
[ 55] 0x00007fff3d610efd D:\Program Files\MATLAB\R2021a\bin\win64\dig.dll+03411709 dig::ActionCallback::operator()+00000029
[ 56] 0x00007fff3d5027d4 D:\Program Files\MATLAB\R2021a\bin\win64\dig.dll+02303956 dig::ActionService::executeActionImpl+00001732
[ 57] 0x00007fff3d50185f D:\Program Files\MATLAB\R2021a\bin\win64\dig.dll+02299999 dig::ActionService::executeAction+00000287
[ 58] 0x00007fff3d501e64 D:\Program Files\MATLAB\R2021a\bin\win64\dig.dll+02301540 dig::ActionService::executeAction+00000388
[ 59] 0x00007fff3d505e71 D:\Program Files\MATLAB\R2021a\bin\win64\dig.dll+02317937 dig::ActionService::hasUnmappedActions+00002657
[ 60] 0x00007fff3d49b9f3 D:\Program Files\MATLAB\R2021a\bin\win64\dig.dll+01882611 dig::config::Widget::Impl::printHierarchy+00037091
[ 61] 0x00007fff3d4af2f0 D:\Program Files\MATLAB\R2021a\bin\win64\dig.dll+01962736 dig::config::Widget::Impl::printHierarchy+00117216
[ 62] 0x00007ff810b5392a D:\Program Files\MATLAB\R2021a\bin\win64\iqm.dll+00801066 iqm::PackagedTaskPlugin::execute+00000074
[ 63] 0x00007ff810c7e1ed D:\Program Files\MATLAB\R2021a\bin\win64\mcr.dll+00516589 services::lmgr::exception::LicensingStartupException::~LicensingStartupException+00009613
Last resort exception handling: force closing 'vehicle21'.