Hi Manuel,
I agree all WPs are waiting for "commit" is the source of the problem. However, I can't identify is it caused by a bug of SAP kernel or a custom program? Sorry, no offense. Is it possible a custom program causes all WPs stop at "commit" for a couple of minutes? I don't think so.
By the way, "ZRSCMSTU" is a report to check if a user is a valid login or not using USR41(user-terminal).