3251: instance.generate() leads to "NSArray was mutated while being enumerated"

Hello. I was trying to find the issue in my plugin code, but it appears this is an issue with Glyphs. In 3250, exporting with my plugin works fine, but in 3251, I get this error:

NSGenericException - *** Collection <__NSArrayM: 0x60000b339200> was mutated while being enumerated.

Check Macro window output.

Georg, you have access to the export plugin repository.

Can you send me a font and a screenshot of the report settings?