Remove the rubbers and put them back on 'upside down' from the way they are now, see how it goes.
Maybe if they're old/worn they're a little harder and slip along the flipper paddle as compared to new rubbers that would have more friction-grip onto the flipper-bat, as the others said "grab some newbies".
Is it also likely that you (or previous owner) may have lubed the flippers which has made it's way onto the flipper bats over time? maybe cleaning products on the playfield has done this?
Are the flippers slightly tapered to allow the rubbers to ride up maybe?
my 20c
MM.
