No idea why ... out of warranty and have read that parts are too expensive to even bother.
I had the Dynamic which I really liked with the dual motors. Had a power supply replaced under warranty, now it just seems to twitch once and nothing.
Got the Diagnositic from in-laws who hardly used it after mine stopped worked for a couple years and now seems to not to anything.
Both are about 5-6 years old now, but given the trend, seem to only last around 3 years in a pool open year round.
I can only guess water intrusion. Have not gotten around to opening them up and checking them out. No service center near me to check them out and certainly not going to ship them.
What I did not like about them was the bag/diaper. Worked great at filtering the water, but annoying to have to clean, plus you had to tip it upside down in the water before you pulled it out or all the junk would fall back into the pool. The newer top loading models look better and may be less hassle with a cart filter. But, they also cost 4 times as much as a suction cleaner (looking at a used PoolCleaner). I could buy a new suction cleaner every year (even though there is not much to fail) for less than the cost of a robot if it is only going to last 3 years.
True with the suction I would have to clean the filter more often, so that is a hassle as well. And maybe I would have to run the pump longer (although doubtful).
IDK ... I am torn and rambling. I just know that my pool is cold and getting dirtier because my cleaners are dead.