Hi @RogueSteward,
What xbox controller are you using? Flaps, should already be configured on most - xbox one or newer.
Above each trigger is a button. Left button is for incremental flaps up. Right, incremental flaps down.
If you are changing these assignments, you’ll need to delete the defaults. I have notice, like you wrote, that some of these multiple button combinations don’t register.
However, I’ve never tried duplicating the default controller and removing all assignments and start over with my own.