Im using mayflash 4 port adapter and the shield button always ends up inverted aka when im not holding anything I shield, and when i hold L+R I stop shielding. This happens using the button and both the + and - of the analog part of the trigger.

Make sure that in the button assignments, whatever you use to shield is set to a button not an axis. The best way to make sure you set this up correctly is to press the trigger almost all of the way down, then press the shield button in SSF2 (brings up the input screen) then you press the trigger for that final click. It should be set to BN something as opposed to AX something. Do this for the other shield and trigger, hit "Back" to save your changes, then I think you have to restart SSF2 to make the changes take effect.

Let me know if that doesn't fix your problem, but I feel it should. This is a common issue.