In my experience with Ancestry support, you have to do a lot of hand holding when it comes to issues with FTM. They'll do whatever they can to get rid of the ticket as quickly as possible, and you have to ride them to see the problem through to a solution--if one is possible. They are not given incentives to solve problems. They are driven to close tickets.
If you are able to recreate this problem, then tell them to recreate it. If there is a bug in the software, the onus to prove it shouldn't be on you after you've explained how to recreate it.