I have the open air model and it does this same thing, been dealing with it for 2 yrs. and came looking for an answer.
Hi @Drask and welcome to the forum!
Based on your description, that the robot doesn’t stop turning, you should check two things.
First check magnets (https://community.robotshop.com/blog/show/litter-robot-iii-open-air-the-secret-behind-the-globe#Magnets%20for%20tracking%20the%20position).
If they are fine, I would suggest replacing Hall-effect sensor. Read more here: https://community.robotshop.com/blog/show/litter-robot-iii-the-hall-effect-sensor