#7 in Player List of Known Issues
When you encounter this bug, try running away. Let the mob follows you far away. Then run back to Urshi as fast as possible, leaving the mob behind.
Also, the mob won’t follow you to next floor. You may go to next floor. Then teleport back to town. Use the portal in town to go back to 1st floor. Then run to Urshi. I know, it may be a long way, but you are safe.