Some light reading on eos switches in modern games
http://docs.missionpinball.org/en/latest/mechs/flippers/eos_switches.html
The main idea is here from forum user homepin in another thread:
The EOS switch in modern machines is really only there in case a super fast ball slams into the flipper while it is being held in the up position.
1. press flipper button and main pull coil activates, pulling the plunger swiftly to the upwards position.
2. the MCU starts a timer counting while at the same time the MCU "looks" for a closure of the EOS switch.
3. one of two things now happens here:
A. the MCU sees that the EOS switch has closed - or
B. the timer times out and the MCU "assumes" the plunger has now made it to "flipper up" position
4. the MCU turns ON the hold coil and then turns OFF the pull coil holding the plunger safely in the up position.
The problem now is if a fast ball slams into the flipper the MCU has no way to tell if this event has happened so the flipper will very likely flop to the down position as the hold coil won't have the power to resist EVEN IF you are holding the flipper button ON.
If the EOS switch is intact and working correctly, the MCU would "see" the EOS switch go open and say to itself: "wait a second - the flipper is held in the up position - that's not right" and so the MCU will pulse the power coil again to make sure the flipper remains in the up position.
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I read conflicting info on how whitestar uses eos switches, but if they are programmed to cut pull power after a time limit or eos is closed, whichever comes first this could be your problem.