A couple of years ago I opened a case and found a lot of hairs had broken at the end where the bow tucked into the holder. That was definitely a clothes moth situation because I found the dead moth, from what I've read it's the larvae that cause the problem because the adult moths don't feed.
Last year I had a problem with 2 bows which had recently been rehaired. They were in daily use and not left in the case, and each day I would find a few hairs had broken, in the same area. There was no sign of any bugs, and after a while there were no more breakages so I didn't call the person who did the rehair. When I next take the bows for rehair I'm going to ask if he's had problems reported with that batch of hair but it could be that other people,like me, have had the same experience but not felt it worth telling him.
Would it be worth contacting other people who had rehairs at the same time to see if they have had breakages?