Since the device has not been changed long ago, there may be a problem when the QHY driver is updated.

I thought the same thing when my problem occurred - the first time it worked fine, then an update and now it doesn't work - but since I've used the small computer once I changed mind. I or someone with better experience (I never compiled a C program) should try compiling an old version of indilib to test it, maybe on both your Raspberry and my PC.
Kind regards,
SB.

I have not checked it yet, but probably, if I use RaspberryPi 3 which I have not updated, I think that the problem of the QHY driver will be gone.
However, since it does not become a fundamental solution, I hope that the problem will be solved by updating the QHY driver.

Yes, maybe looking at the changes made from the working version to the current we'll be able to find the mistake. Try using the QHY with the old version, while I'll build it from the git repo.

I tried the older version of the QHY driver with RaspberryPi3.

Running 5 seconds X 3 times from Ekos did not give any problems.

The QHY driver version is 1.7, the interface is 2.2.

Good! I'm building libindi, commit 82499d580f2dd529d4571a9ea7a1ac857357c223

Interesting update: I successfully built INDI (using that old commit) on my target computer using all the commands found in the GitHub repo's readme. Before doing that, I manually removed all the files installed by the QHY SDK in my system and all the INDI/KStars/fxload dependencies. I built all the 3rd party drivers and then, since fxload was not included in that commit (I wasn't able to boot the CCD), I had to build the latest from HEAD. Then I installed the QHY firmware files, udev rules and shared libraries (not the SDK's fxload) from the QHY Linux repo, but using version 1.0.2 instead of 1.0.8, which seems to support 32-bit computers - only today I saw that the current repo only contains version qhyccdsdk-1.0.8-Linux-Debian-x86_64.tar.gz. SDK version 1.0.2 is also a version pretty close to the one used in the commit I compiled (1.0.1). Note that I had to install the QHY SDK after building and installing the INDI sources, due to a strange make error (error code 2, I don't know what it means) occurred while compiling the QHY drivers. Everything installed fine. Rebooted and connected the camera, which now boots correctly every time, so the fxload is doing is job. However, when I started the INDI Web Manager and, using it, the indi_qhy_ccd service, another error occurred: the service is not able to find the camera, although it's ID in lsusb is 1618:0921 (see posts before, it indicates that everything is OK). Remote KStars shows the same error.
If a INDI developer thinks that I made a mistake while building I can provide further information.
Don't know what to say.@T-Studio do you know which version of libindi your Raspberry uses? It shouldn't be very old: the small computer worked fine before Xmas.
I'm doing other tests to get some logs.
Kind regards,
SB.

Edit: it wasn't able to get any log: my remote KStars isn't reporting any error (only that no QHY is found), so I'm not able to access the INDI Control Panel to get other information as described here . indi-web is not reporting errors even with --verbose. Just no QHY found.

The old version of libindi that worked

1.5.0+r3494~201710221602~ubuntu16.04.1

Thanks!
Since the INDI library I built didn't work, I removed it usingThen I looked at the oldest indi-full version available in the package managerAnd installed it manuallyNote that I've also tried installing the current release but it did't work, too and that the oldest release available may vary depending on the Ubuntu version. Unfortunately, the camera now works with 5...7 seconds exposures, but not with 3.5 seconds or 10+ s. No way to get an older version from the repo Any idea? Does anyone know the commit that corresponds to version 1.5.0+r3494~201710221602~ubuntu16.04.1? ThenWill help us.

The one that worked properly in my environment with the QHY driver is as follows.
libqhy
1.0.1+r3494~201710221004~ubuntu16.04.1

indi-qhy
1.7+r3494~201710221347~ubuntu16.04.1

I attempted to downgrade from the current version, but unfortunately the older version does not seem to be present in ppa.

There is no choice but to wait for the developer to solve the problem. .

The AP - 34 contains the latest QHY drivers, but this machine did not work on any exposure.
Other drivers are functioning properly on AP-34.
The new QHY driver may be faulty depending on the system.

(I have not tried OrangePi yet.)

The common symptom is that the driver normally starts up and is recognized, but the count of exposure will not be changed at the time of downloading after shooting, it will be unusable unless the camera is turned off and the driver is restarted.

Is anyone still interested in this topic? My QHY still doesn't work..