recently this problem too. I had one bent spindle. Further, the deck pitch was way out of whack.
For the spindles, turn the blades and see if the tips line up. If the blades don't line up the blades or spindle could be bent. Best to put on brand new fresh blades.
Follow the directions in the owners manual for leveling the deck.
I about guarantee this this will fix your problem.
Check tire pressure too.