thanks for your input! This made no difference -however, apparently updating the firmware to v5.10.3 did help. I hope the issue stays resolved this way.
The strange thing is that we had no problems in the 2 prior months of testing?
Sorry for the big thread with an apparently easy solution. As long as this can help others or the further development it was not worthless though :-)
You're very welcome! I was asking about the FPS reduction because when there are 'USB REC' type errors, a reduction in resolution or FPS usually fixes it. And you could not go lower in terms of resolution.
If you have problems in the future, especially when using multiple cameras, a user in the past with a multi-cam setup (up to 4 cameras) found that they could run their application for long periods if they used an industrial-grade USB hub.