Changing the engine quality settings to low or medium will cause the editor to crash
This was tested in 4.24.3 @ CL 11590231 and doesn't occur, so this is marked as a regression.
Mac Environment
Operating System: OS Catalina 10.15.2
Version 10.14.6 (27-inch 5120 x 2880)
Model Name: iMac Pro (2017)
Processor: 3.2 GHz Intel Xeon W
Memory: 32 GB 2666 Mhz DDR4
Graphics: Radeon Pro Vega 56 8GB
XCode: 11.2
Expected Result: Engine settings would go to low or medium.
Result Engine Crashes
Assertion failed: !Material->IsDefaultMaterial() [File:D:/Build/++UE4+Licensee/Sync/Engine/Source/Runtime/Engine/Private/Materials/Material.cpp] [Line: 335] UE4Editor_Core!AssertFailedImplV() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\Core\Private\Misc\AssertionMacros.cpp:100] UE4Editor_Core!FDebug::CheckVerifyFailedImpl() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\Core\Private\Misc\AssertionMacros.cpp:450] UE4Editor_Engine!FDefaultMaterialInstance::GetMaterialWithFallback() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\Engine\Private\Materials\Material.cpp:335] UE4Editor_Engine!FDefaultMaterialInstance::GetMaterialWithFallback() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\Engine\Private\Materials\Material.cpp:339] UE4Editor_Engine!FMaterialRenderProxy::UpdateDeferredCachedUniformExpressions() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\Engine\Private\Materials\MaterialShared.cpp:2590] UE4Editor_Renderer!FPrimitiveSceneInfo::CacheMeshDrawCommands() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\Renderer\Private\PrimitiveSceneInfo.cpp:218] UE4Editor_Renderer!FPrimitiveSceneInfo::AddStaticMeshes() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\Renderer\Private\PrimitiveSceneInfo.cpp:548] UE4Editor_Renderer!FPrimitiveSceneInfo::AddToScene() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\Renderer\Private\PrimitiveSceneInfo.cpp:710] UE4Editor_Renderer!FScene::UpdateAllPrimitiveSceneInfos() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\Renderer\Private\RendererScene.cpp:4075] UE4Editor_Engine!<lambda_5b722a40972cf3fb98161bec545a6a93>::operator()() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\Engine\Private\Components\ActorComponent.cpp:105] UE4Editor_Engine!TEnqueueUniqueRenderCommandType<`UpdateAllPrimitiveSceneInfosForScenes'::`2'::UpdateAllPrimitiveSceneInfosCmdName,<lambda_5b722a40972cf3fb98161bec545a6a93> >::DoTask() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\RenderCore\Public\RenderingThread.h:195] UE4Editor_Engine!TGraphTask<TEnqueueUniqueRenderCommandType<`UpdateAllPrimitiveSceneInfosForScenes'::`2'::UpdateAllPrimitiveSceneInfosCmdName,<lambda_5b722a40972cf3fb98161bec545a6a93> > >::ExecuteTask() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\Core\Public\Async\TaskGraphInterfaces.h:849] UE4Editor_Core!FNamedTaskThread::ProcessTasksNamedThread() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:692] UE4Editor_Core!FNamedTaskThread::ProcessTasksUntilQuit() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\Core\Private\Async\TaskGraph.cpp:587] UE4Editor_RenderCore!RenderingThreadMain() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\RenderCore\Private\RenderingThread.cpp:341] UE4Editor_RenderCore!FRenderingThread::Run() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\RenderCore\Private\RenderingThread.cpp:472] UE4Editor_Core!FRunnableThreadWin::Run() [D:\Build\++UE4+Licensee\Sync\Engine\Source\Runtime\Core\Private\Windows\WindowsRunnableThread.cpp:76]
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-89698 in the post.