That sounds pretty comprehensive! The only thing I don’t see you mentioning is running Anki without add-ons to see if you get the same result.
I’m not familiar with that one. If it’s doing anything non-standard with the files when it localizes them – that might be worth looking at.
There have been a few similar-ish reports lately, so check if any of them suggest things you haven’t thought of yet. Other than that, this sounds like something @dae will know a solution for, or a step you can do differently.