Hi Mona,
I noticed the same behaviour with the mopping module. We changed the water filters, because we guessed that they might have clogged since we had very calcareous water. Afterwards it got better, but not as good as in the beginning, i.e. the mop does stay wet but only a little water is used from the tank. My next guess was that it could be the lower temperatures at the moment, so I was waiting for summer to see if that changes.
Once my vacuum didn't want to clean any longer, it would just move one meter, turn around and return. After looking at the map, I noticed that it thought that the door leading from the base station to the main corridor was closed (because it was the last time it was cleaning) and so it didn't want to pass through the now open door. What helped was setting the robot to only clean the room it was in (with the door open) and then it updated the map and next time it would pass through again.
Another problem we had was when we switched from a bed that was on the floor to one on legs, the robot didn't want to clean under the bed. The thing that helped here was deleting the map and letting it clean the whole apartment and thus create a new map. Now it cleans under the bed without problems.
Hope these experiences help.
Cheers,
David