Thank you for the explanations!
Even if my problem might have something to do with SC 3.3, it is a bit off-topic here - sorry.
Yesterday I wanted to observe an occultation. Again the image froze when switching to 16bit mode. After restarting the camera and SC (3.2.6433.0) I could use 16bit, but it was still faulty. I got an bright zone on the top of the image:

I guess the QHY-drivers are damaged in some way. I know, it's a bit tricky with QHY-drivers: One must not use the wrong version...
On https://www.qhyccd.com/download.html they offer a "System Pack". I'm not sure that this is the correct choice, but there isn't an alternative on the web site.
What would you recommend for a fresh installation of the whole package?
Cheers,
Niko