The problem is not with the handle or chain.
For some reason the flapper is being ‘sucked’ with a lot of vacuum into it’s seat.
It takes a significant amount of strength to pull the chain hard enough to lift the flap….sometimes you have to grab onto the flap directly in the tank and ‘peel’ if from the flapper seating.
The rest of the toilets in the house are NOT this hard to flush.
Any idea what could cause this?
Thanks.