Thanks, will try that.
I think I tested every combination yesterday with the 4.c version and for me the only way to mine without random (silent) crashes is the compatibility mode. So it looks like this:
dual workerID + compatibility mode: no problems, but always stays at the funded ABN (doesn't change back, even with unlocked wallet and enough abnweight)
dual workerID + legacy Win10: random silent crashes
1 worker ID + compatibilty mode: no problems, runs with non-funded ABN
1 workerID + legacy Win10: random silent crashes
btw: I don't have a restored wallet. Today in the evening I'm gonna try the 4.d version.