It could definitley be a number of things. But I had this happen on my acdc not too long ago. Mine was a bad coil stop. When the stop gets loose, it tears up the brass and then the stop touches the steel bracket and completes a magnetic circuit so the plunger sticks to the stop. The giveaway for me was there was lots of shiny brass dust under the flipper mech inside the cabinet. If you see a bunch of this shiny brass dust, you know that's the problem.
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