When I initially started using the Kstars/Ekos/Indi environment a few years ago I worked with a Fuji X-T2 mirrorless camera and a ZWO 120 mini guide camera controlled by a Raspberry Pi 4 (Astroberry) at the telescope with Ethernet to my laptop. I had a lot of issues with cameras staying reliably connected. This issue was solved when I added a powered USB 3 hub (12V) and plugged the Fuji into the hub and the ZWO mini into a USB 2 port on the Pi.
When I added a QHY268M last fall I just unplugged the Fuji and added the QHY camera - all was well. A few weeks ago I attached the QHY camera to an old Hasselblad lens (50mm FLE from a previous life) and mounted it alongside the ZWO mini/guide scope setup on a 300mm D-type rail. I used this along with the existing bracket holding the USB hub, SSD, RPi from the telescope setup. It all worked until a few days ago when I made a new, smaller bracket to hold the electronics. Then things started getting flaky. (On top of this, I had a new laptop (Linux/MacOS) as my old (though newer) HP (Linux/Windows) laptop died (completely) - so a new install of Kstars. Being in the mioddle of a rare string of clear nights I was anxious to make the most of these (essentially) moonless nights (~49 degrees north, so short "nights"). After last night's fiasco I approached the issue more methodically than I had to this point, when it finally dawned on me that I had plugged the two cameras into the same hub (because in the telescope setup there were three items plugged into the hub. I'm not using the ZWO-ASI focuser... duh.
This afternoon I moved the guide camera back to the RPi and all is good again. So, tonight should be more productive.
Moral of the story, for me at least, is: where you plug the USB cables in matters. (i knew that once, but seem I had forgotten it)