A quick update: I found the issue.
The new version of the dnd5e system hasn't changed its format as far as I can tell, but it does a TON of checks now for missing and empty values which it didn't care about before. This means a lot of changes under the hood of the converter for just about all conversion stages.
I'll have to implement the fix in a few stages:
- Add lots of empty strings and null values all over the place as placeholders until the import in Foundry works for a single character.
- Create 10+ characters and test if the import works correctly while finetuning and rewriting parts of the converter
As this touches upon most of the converter code, it will take me a while to get the converter to a semi-stable state again and I have a feeling it will introduce some bugs here and there. I'll create a post to warn people not to update to 2.1.5 for now.