The reflex unit is part of the circuits that award increased scores and features. The reflex unit tightens up as the player wins games, and loosens up as the player spends credits or coins. Some operators hacked this unit by re-orienting the wipers on the reflex unit such that the wipers connected to fewer rivets than as was designed by the factory. The result is increased profits for the operator because increased scores and features are awarded less often than they otherwise would be awarded.
Here is my write-up, with extensive photos, for how to detect if your reflex unit has been hacked, and how to return it to as it was designed.