Hi man, and thanks for your reply.
Yes, I was talking about the Variax 700 electric, but somehow missed to mention it explicitly. The old/original firmware version was 1.31, the new ones are the ones you mentioned: 3.05 and 3.10 which both have the identical problem.
The thing is that the update process itself went well—on a MacOS through Pod HD. It was a 'success' as a process, but definitely not as a result.
Just for notice, I am using a significantly-dropped tuning from A: a e a d e a. But it was the same tuning before the update as well, and there was no muffling or distortion whatsoever. Now all 12-string patches are broken, regardless if I choose one from the factory ones or make one myself from scratch. I think the chime sounds are also broken a bit.
Can anyone help with the original firmware version please?! I'd greatly appreciate it.