I am switching from an rPi4 running stellarmate to an ASUS pn51 mini pc since the rPi4 struggles with firecapture and the downloads from my QHY600 are 120MB FITS files which stress the rPi4 also. I have the pn51 running ubuntu 20.04 and booting directly into an account with vnc running so it behaves similarly to stellarmate with kstars 3.5.4 stable. When I first hooked up the QHY600, once I figured out I had to update fxload, I could take some dark frames and they downloaded about 3-4x faster than the rPi4 at 0.5 sec which was good news. However, after the first couple of images it stopped downloading. It counts down the image duration then just sits waiting to download. First thing to do is check the log files so I enabled verbose logging for Capture and CCD. Seems like there are USB issues. I have rebooted system and restarted kstars multiple times but have not been able to restore successful downloading. logfile attached.
I wish I had a solution for you. From time to time I have the same problem, with an SBIG camera. It exposes, then when it comes time to download it just sits there with some fraction of a second in the timer window. It happens to me rarely, but when it does, the only thing I've ever been able to do to get it working again is close Ekos and Kstars (the disconnect and stop buttons don't usually work), then VNC into the RPi and stop Indi. When I load it back up it almost always works. Very rarely I have to reboot the RPi. Not a solution for you, and probably a completely different problem, but same symptoms.