Would have thought this kind of scenario would be considered an Airworthiness issue as the TCAS availability is not fully available as per design. If stuck in ABV then only threats between if I remember right -2700ft and +9000ft would be displayed.
So personally would apply the MEL that renders the TCAS system inoperative and get a TCAS control panel ordered ASAP.
Making it a NEF (non-airworthiness item) would likely result in repairs not happening too fast as in my experience material/logistics departments often don't react too quickly to this kind of deferred defects/hold items.