Quoted from Oldgoat:
It's interesting. I had this exact same issue. Out of nowhere, the right flipper started hanging up. Couldn't find any rubbing anywhere. So, I cleaned it up, replaced the coil sleeve, re-positioned and tightened things up, adjusted the flipper, etc. None of these actions seemed to be addressing any noticeable problem; however, in the aggregate, viola, everything was fine. I'm confident that 90% of what I did was of no benefit. If you figure out the exact cause, let me know. I always hate it when something that was broken starts working but you have no idea why.
Make sure you have the proper gap between the flipper plunger/crank assembly and the plastic bushing that the flipper shaft sits in. They actually make a small plastic gauge for setting it properly. If it's not gapped properly and it's too tight it can cause binding.