Mixing doesn't work on 12.1?

[UdjinM6]

Ok, yes, bugs in software are unavoidable at some point. Is there anything else I can do to help? File the bug in an issue tracker somewhere? Any other information that is helpful to resolve the issue?

I'm working on it. I made first attempt to fix it https://github.com/dashpay/dash/pull/1364 but it looks like there is smth else.
I don't think there is anything you can help with, I guess I just need to cleanup some things first and re-think the process a bit and then implement it correctly. Half way there I'd say...
Thanks for reporting and sorry for inconvinience!