I don't think its heat. I used two different backs, and two different films. One that was stored pretty carefully, the other was in the back for 6 months+. Both are fogged in the same way, a bloom from the top like the paper was leaking light from one side. However, that cannot be what happened since I'm using two backs, two different rolls of film, both removed from the back in the darkroom. I've loaded many many rolls of film in this room, and this is the first time I've had a problem. The only new thing is the enlarger with the glow in the dark disks.
Perhaps I'll take 2 film strips from a bulk roll and develop one after waving it by the glow in the dark disks, and develop the other without... It sucks, because we had an nice storm last night and I took some really nice shots of the ice on the trees 🙁 Doesn't happen that often!