After upgrading to 4.2 my group promotion settings that I had for years have disappeared. Has anyone had the same issue?

Adding them back is easy, but the problem is, I don't know when exactly they were removed and I don't know what and how many members haven't been promoted. IPS should really warn about stuff like that.

4.2 includes new group.promotion criteria, which probably wiped out your old ones.  The upgrade should have kept them.  You should submit a ticket and provide a database of your 4.1.19