Yeah, you’re right, most likely some plugin. I had another project now which didn’t show this behavior and I just tried and audio-only project with just using cubase channel strip, no problem. It is weird though that it only happens after some time. Or some action, that is.
The problem is now finding out which plugin is the culprit… I’ll try using listddls to find out which dlls are still loaded, but if anyone has a better idea, let’s hear…