It seems like a player's pet monsters might not follow them to a new location on the same map. I am at Resir's House (/scorn/houses/resir). It's a single map with upper and lower floors separated by "blocked" tiles. You 'a'pply a hole at the back of the top level to get down to the next level.
Pets down seem to follow the player "down", and stay on the upper level.
Probably when a player applies a teleporter we want the pets to follow the player, even if that just means a new location on the same map.
Should be patched in d82d758218ba097d531a30436ea261bc1efc1d18, thanks for the bug report :)