Our did this at our old place, and it turned out that the tube behind it was getting a little bit squooshed! Someone must have bumped the front of it, and pushed the whole thing back a tiny bit - less than an inch - but it was enough to slightly crush the pipe thing, and voila - apparent blockage.

Heaven only knows how many times we cleaned and recleaned the filter, the arms, the inside, the door, the seal, and ran vinegar and finish and whatever else runs through it before we realised what had happened ... !

Pulled it out, straighted up the tube, put it back in with room for the pipe to remain uncreased, and it was good as new.

And terribly, terribly clean!