In the past I've witness potter's angels refuse food despite being offered a wide variety. They eventually waste away and perish. I believe collection practices most likely aren't the root cause because they are only found around the Hawaiian Islands and Johnston Atoll. Haling from US waters, means they are most likely hand netted.
I've been told by US wholesalers and collectors that the majority of Potter's are collected at slightly deeper depths than typical reef fish. I'm not certain if you could actually refer to them as "deep water" reef fish, but I don't believe they are common at the surface like flames are. Whether they suffer from decompression complications is difficult to say but seems plausible.
Perhaps they are just a sensitive species, much like regal angelfish and Moorish idols. Although, for the record, I don't think potter's are quite as difficult as these two species. However, some of the regals that I've kept that pulled through and became very solid fish eventually, had touch and go moments in the beginning. It very well could be possible that potter's angelfish just aren't as durable as some of the more commonly encountered species.