Late reply but turns out the issue was a case of user misuse (isn’t it always )
Long story short, the Alt Launcher UI doesn’t reflect the inversion of the throttle properly when the axis is inverted. So setting the AB detent at 80% showed it was in idle cutoff (or something like that, showing the wrong detents in UI even if they were set properly. Naturally I was trying to ‘reverse’ the detents to get the UI looking right, which set my detents up backwards and caused this weird issue
Looking in game you can check the real detent settings, although they should be set in the alt launcher and not the game since the change will not persist otherwise