The coil is then good.
When you swap left and right, does the left flipper then fire ? In test you see on the switch matrix when the button is pressed but not the EOS. You mean when you lift the flipper manually ? Because if the flipper does not fire after pressing the button, there is no way the EOS can be closed. If the EOS closed is not shown on the switch matrix in test mode, after manually lifting the flipper, the EOS is bad and should be replaced, or the EOS wiring with the fliptronic might be broken somewhere.
But it should not be the issue for a flipper not or weakly firing, as power and hold voltages are managed by the fliptronicII and power voltage should not be impacted.
What is the voltage between the coil lugs (center and blue/yellow wire) after pressing the button. Do you get 0 or close to, or 50 vdc ? If 0 or close to, have you checked Q3 ?
Then Have you cleaned the optos ? Are you sure the EOS is Normally open and closes at the very end of the flipper course ?