The main camera hangs up randomly somewhere between exposure and download. When it is used alone it tends to hang up not so often. If you start the guiding camera (in loop) at the same time the hanging up of the main camera manifests immediately (at the first few exposures). At first, I suspected a power supply problem, but I powered the main camera from an independent power supply (powered USB hub) and the problem remains the same, so it must be a software problem.
Try to set a lower resolution in the INDI Control Panel --> Controls, does this help? If yes, then this is a known USB issue with Toupcam and all touptek based cameras on Raspberry PI.
The only resolution available for this camera is 1920x1080. The only thing that I could do is to increase binning.
On the other hand, if this is a known USB issue with Toupcam and all touptek based cameras on Raspberry PI, may I ask you if this a software problem (potentially solvable) or is a hardware one and there is no possible solution ?
It's a software issue in the SDK. I tried reaching out to Toupcam several times to get a solution for this but no response. You should contact them to raise this issue.
I've contacted support of astroshop.eu, the guys I bought the camera from, and they are saying Touptek updates their SDK frequently and that the last update was on 2020-02-24. Is that true ?