> I did some more research while I was fixing some of the keys.
First of all, you have done some excellent detective work trying to isolate the cause of the problem.
Second, I am not a DIYer and have almost no experience with diagnosing and/or repairing issues with electronic circuits.
Third, that being said, you reminded me of the zipper effect I had when I used my CZ, probably the CZ-5000, though it could have been a CZ-3000 or a CZ-1. I don't remember if it went away on its own or if it went away when I rearranged my gear, my midi routing/connections, or my audio connections.
It was most noticeable when I scrolled either one or both of the wheels (I don't remember which as it was decades ago).
I remembered this when you mentioned at the end that it seems clearly to be related to midi data.
I know its not much, but maybe it will help with further isolation of the conditions that contribute to the zipper effect.
Steve