Thx for your reply.
The device times out. There are no miscalculations reported, neither before not getting any results nor while it tries to recover. Looks like this:
[...]
Antminer (COM9) ERROR: Selftest error. Timed out at 25000 ms.
Antminer (COM9) ERROR: Selftest error. Timed out at 25000 ms.
Antminer (COM9) ERROR: Selftest error. Timed out at 25000 ms.
Antminer (COM9) ERROR: Too many errors, giving up
As I said when starting the device manually again it does work. I will try to setup some regularly scan intervals to get it back up.