Press the plunger down all the way till it stops with your finger, and make sure the switch gap opens to EXACTLY 1/8" (3.2 mm). Not more, not less.
You may have to fiddle with the leafs to get them strongly touching when relaxed and 1/8" gap when plunged, but it is a lot easier to do on the bench than installed in the game. You will get the hang of it, take your time and get this exactly right.
As the gap opens, the stationary half of the switch leaf should move towards the other contact. Literally the two contacts should always spring towards each other, not just limply touch.
If your flippers don't hit absolutely hard when you power up the game again, 99% of the time you somehow messed up the EOS gap, and the contacts are not touching with enough force.
You can jumper the two leaves of the switch together with alligator clips as a test when diagnosing weak flippers, if the flipper now kicks like a mule, the switch is not properly making contact, is dirty, or is broken.....at least you know where the problem lies.
Make sure you install the left and right mechs back onto their proper sides and you are ready to play your game how the designer intended it to play.