Hi Götz,
actually for testing went down to pretty minimal picture sets - like 60, where I previously completed projects with more than 400 successfully.
I don’t believe there is a hardware problem - it’s a solid, recent Alienware notebook that should be good for that task and handles similar intense jobs without issues.
I so hope in the end it’s not some stupid thing I am doing wrong - otherwise, I owe all you guys big time for causing so much fuzz 
but I am really clueless by now