I managed to do some further tests (tested the camera on two other devices and it works fine), also swapped various components (raspberry, power supply, SD card...)in the setup just to rule out a hardware issue.
I did however manage to finally get something that may give a clue to the contributors of indilib.
I have the full stack that comes after that if required for further debugging, but it does look like the indi_asi_ccd did something wrong, I wonder if it is because the ASI385MC is not really handled by it.