Hello there @WeberSystems!
Checking through your log, it sounds like the cook procress is stumbling with a broken blueprint, considering the line below:
Assertion failed: IsThisNotNull(this, "UStruct::IsChildOf")
File: Class.cpp Line: 2758
UE is tacking with a null reference, most likely due a blueprint not properly updating to 5.6.1. So, the easiest fix would be to run “Validate Assets” on your Blueprint folders and watch for failures. After that, you can force a clean compile for any affected elements (select aBlueprints, right-click > Reload, then do Refresh All Nodes, recompile, save).
It would also help to clear your project’s cache, via closing UE, and deleting folders Intermediate/, DerivedDataCache/, and Saved/ from your main directory, then allowing UE to rebuild. After that, try to cook again.