I've just received this response to a support ticket:

"...unfortunately we don't have a report or way to set a notification when a family encounters the non return contract issue, a contracts list is the best you could get.. You can filter on contracts that have not been submitted or at least have the submitted and processed status, but not if were successfully submitted but not returned."

It would be wonderful if there was a way to view these errors, because they can be easy to miss without a dedicated notification or spot to look for them.

Thanks!