Assert failed/crash - property 'Debug' belongs to class "Trash"

Unreal is crashing on me a lot - perhaps every hour, with an error like:

Assertion failed: ((UObject*)ContainerPtr)->IsA((UClass*)GetOuter()) [File:D:\Build++UE4+Release-4.16+Compile\Sync\Engine\Source\Runtime\CoreUObject\Public\UObject/UnrealType.h] [Line: 351]
‘WalkToTarget_C_0’ is of class ‘WalkToTarget_C’ however property ‘Debug’ belongs to class ‘TRASHCLASS_BeetleTask_629’

I’ve tried rewriting these classes and it’s still having a problem. I’ve also created a new behavior tree and that hasn’t happened either. I’ve Googled and seen that other people have had this problem in the past ( but so far nothing has helped.

I haven’t tried it with a vanilla project because it’s too time-consuming to bring everything over into a new project.

P.S. I’m an experienced game developer but new to Unreal.