ToME: the Tales of Maj'Eyal

I haven't played Sandworms Lair since it had the old layout with a lot of tunneling worms. So I enter the Sandworms Lair and follow the giant tunneling worm for a couple of minutes and kill enemies along the way. Then I stepped onto a tile he was about to move onto and he disappeared. Luckily I was in a safe zone in the sand, but I used Rod of Recall to re-enter the Lair and there weren't anymore tunneling worms, so I couldn't get to the end of the tunnel.

Also I went back to the Old Forest and, in a completely cleared area, I got an escort quest for some reason. There was also a random encounter in that level that I'd done before and it was reset.

The escort appearing in a cleared area is normal - if the escort can't find a way to the portal the first time you enter (normally due to a closed door), they won't spawn, but when you return they likely will be able to find the route now and will pop up.