Thanks for your report. I will fix this before I push GodoRogue to Steam (for free). Killing that venustrap will free you.
Oh, i believe i may have found the reason the softlock happens.
if you are on the stairs and a monster is next to you, it actually manages to attack as you descend.
either descent takes 2 turns or their still coded as existing after you go through a floor, and they hit.
also. the effect of the attract monster and teleportation rings persist even after removal of the ring from uncursing! could be an interesting idea for a challenge run setting, i suppose, but its a bit difficult to proceed otherwise.