Make sure the flippers are not binding. If they are installed too close to the playfield they will heat up and bind. Grab the flipper and pull it straight up and back down. If it doesn't move up and down at least a 1/16th of an inch or a couple mm, then it is too tight.
Here is the tool made to provide a proper gap when tightening the flipper bat.
https://www.marcospecialties.com/pinball-parts/03-8194