Not likely part of the issue, but make sure to clean the flipper button optos too. You'll be right there.

This was happening on my AC/DC. It was the coil stop. The “nub” that goes into the coil sleeve had become loose. Also, that nub can flatten and mushroom over time. When I replaced the coil stop…no more stuck flipper.

Flippers have a crazy number of things that can cause problems!

Almost always with machines like this, you are going to need parts.

Marco sells a flipper rebuild kit:

https://www.marcospecialties.com/pinball-parts/WFLTRON

Replace all the parts in the kit when you do the repair, don't just replace the plunger and leave the original sleeve and stop in place.

I think that when you pull the flipper assembly apart, the plunger will be mushroomed, and a wire edge of metal will be scraping on the inside of the sleeve.

Get some loctite, and use it on the flipper coil stop screws when you reassemble... these coil stop screws have a bad habit of shaking themselves loose!

Good luck!