Crash when loading level in editor

Hello!
For a while now, I’ve been struggling with a crash when loading up a new level in PIE. Basically launching the main menu, then going into a map.

The output is the following:

Assertion failed: !HasAnyFlags(RF_NeedLoad|RF_NeedPostLoad) [File:D:\Build\++UE4\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\UObjectLinker.cpp] [Line: 105] 
Detaching from existing linker for ../../../../../Programming/Foobar/Content/UI/Options/OptionsWidget.uasset while object ButtonSlot /Game/UI/Options/OptionsWidget.WidgetArchetype:WidgetTree_0.ButtonCancel.ButtonSlot_0 needs loaded

Any idea how to fix it? Searching around in google only gives me problems where it was caused by widgets made in older engine version (4.8). I made this widget in 4.20.

Thanks in advance!