Lower filter pressure than normal (without the cleaner attached), combined with lower suction than normal would point to either a suction side blockage or an impeller blockage.
Remove the pump basket and check the pump impeller inlet at bottom and make sure it is clear. If clear move to next check.
While the pump basket is out, put a hose into the pipe inlet near the top of the basket, wrap the hose with a rag and try to seal the hose, then turn the hose on. See if any debris is forced out of the skimmer.
If neither of those works, then the next step would be to disassemble the pump to visually inspect the pump impeller.