I would suggest that the water is not being pumped from the pump to the container.
The 1st check would be the hose/cap connection that feeds into the top of the water container . These can get blocked by small bits of fluff .
Then i’d go with WVM’s suggestion . Check the sump/pump area for fluff build up or something stuck in the drain pump impellor .
There is a very small channel at the rear right of the pump area that gets blocked too.
Get the customer to remove the condensor block and check to see if the area at the rear of the condensor is full of water . This is a sure sign that something is stopping the pump from transferring the water from the pump/sump area up to the water container.