I've had switch leafs that were starting to crack from metal fatigue - they would hold a bend for a short time, then the metal would just give in to the stress at the crack and bend itself out of position again. Just another thought.

Alvin Gottlieb quoted in Michael Shalhoub's "The Pinball Compendium" 1930's to 1960's:

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"A problem that became more serious as the games became more complicated was "contact bounce," which occurred when a switch was rapidly closed. It would occasionally cause the game to miscount the score or not activate a game feature. After seeing the actual bounce using a strobe light and oscilloscope, various modifications were tried to stop the bounce but I decided that a whole new relay was needed to cure the problem. The old relay was just too slow. Doc Garbark, our engineer draftsman, came up with a brilliant design using small tapered switchblades and a lightweight armature. The tapered blades would not have any strong harmonic vibration characteristics and the light armature with its attached switch actuator was very rapid in operation. Doc named the relay the "AG Relay" after yours truly and so marked my place in history. At least to me."

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So, much as we curse the things, perhaps the alternative would have been worse.