Hi @crx978 and welcome to the forum!
Waves have tested, qualified and officially support these processors: Intel Core i3 / i5 / i7 / Xeon / AMD Quad-Core, as stated here.
For this reason we cannot guarantee our software will work as expected with all new processors in the market. I will pass this info to our QA department.
Have you tried this on a blank new session as well? other sample rates?
Well I have far less ram and processing power and can run 4 of them while local recording/streaming in OBS. I do this in Ableton Live 10 (not my favorite version of that DAW). I haven’t used Cubase in decades but it might be the DAW itself? Does it support multi-core performance. Also, Ryzen (AMD) processors get out performed by many of the Intel processors. On paper stats say the Ryzen processors are “better” but there are a few video on YouTube that show otherwise.
Also, try closing the other instances of Mixhub. That might help plus you only need one open to utilize the bucket system.