I've been trying to figure this problem for 2 months and still no solution. Here is my set up that hasn't changed for the past 2 yrs:
Run with low speed pump
vacuum hose instead of KK hose
main drain (through skimmer) plugged
KK Vac Plate
filter pressure is very low, almost zero (with new bigger cartridge filter replacing the old DE)
Everything was running fine until one day, afte a swim, I put the KK back to the pool and next morning it didn't move. The KK was really old with worn out seal and probably gaps in the swivel head assembly. I changed new seal and and head, it moved again but very slow. I bought a new unit (mainly because of the rebate) and it didn't move any faster. I notice when it climbs the wall and when I pull the hose up (not too far from the unit) it speeds up. Cleaning pump basket and filter didn't seem to help much either and no air in the filter, so no leak. And I think because it's so slow (weak suction?) it keeps going in the same pattern (can't fight the weight of the hose?). I had the hose sit in the sun for 2 days to make sure it doesn't coil.
So nothing was changed, why does it slow down?
My other question, which I've been wanting to ask is why is it every time I clean the skimmer sock, the KK runs slower for a day or two until it collects enough dirt/debris in sock. Shouldn't it be faster instead with stronger suction when the sock is clean? It's alway been this way even before I have the problem above.