Why am I getting a fatal error crash?

Looks like UnrealEngine is trying to destroy something that doesn’t exist or is null. The stack trace says it is coming from tick function in daycyclemanager.cpp line 62, and you will also be able to look at the unreal engine source code from there.

I would check that function, your pointers, make sure you aren’t deleting anything twice, make sure you use UPROPERTY() for your class member references.