I had a few hosts that had overlapping interfaces listed in foreman. Not sure how that happened, presumably on fact imports? Regardless, the interfaces were considered to be invalid according to foreman and should be corrected. Easiest way would be to delete them, but doing so resulted in nothing happening. They re-appeared and changes were not saved.

I was able to resolve this, however. If you change the interface and "correct" the invalid value (name of interface in my case) first, then save, you can go back and delete it later.