In addition to Dfly no longer respawning in my world, the following bosses are no longer respawning:
- Toadstool (killed in a copy of the world)
- Ancient Fuelweaver and by extension, Ancient Guardian (the portal is still in its respawning phase animation thing)
- Lord of the Fruitflies (I think, I tried forcing its spawn via lots of rotting crops by reading Horti twice in a row, it wasn't spawning for me)
Antlion, BQ, & Klaus seem to be working
Kill the boss and it doesn't respawn. It's probably an issue related to my world since I loaded it up in the very first beta like in the previous bug report and have been in the majority of beta updates since.