On my Windows 10 machine (small computer, 4 cores, 4 GB RAM) Zorro crashes as soon as I trade more than 1 instance (1 in live mode, 1 in demo). It crashes more or less stochastic ally during every night leaving no error message in the log at all.

Any idea where to search? Antivirus already excluded as reason. No new strategy traded... Worked some weeks before.

Try looking in the Windows Event log for a possible cue.

I like the word "stochastically". But I can not really help, because many things can cause a script to crash or freeze. Follow the hints in the manual under "troubleshooting" and try to catch such a freeze event with the DIAG flag. This can give you a hint which part of the script, or maybe which library on your PC, causes the problem.

Neither event log nor Diag flag recorded any error. At the end a new Windows installation helped :-)