Not sure on this one, but do your working interfaces have 'ip route-cache flow' command on them?
'ip route-cache flow' doesn't show up on any of the working interfaces either.
This may happen if the interface is sending too little data to be worth storing compared to others. Please try to temporarily (couple hours) set NetFlow settings > Top Talker Optimization: from 95 to 99 or 100%. This will force NTA store even small flows, check if you will see data on that interface.
If yes, you can keep the setting, however you will be processing and storing much more data (e.g. 5-10x as much), so make sure you have enough space.
If not, set the setting back to 95 and let us know.