Recently the two center air vents just stopped working. Anyone had this issue? Easy fix?

This is a 2001 IS 300

 

Air flow is controlled by the mode doors, the two center vents should be on the
same manifold as the outer dash pair, left and right. Are they still getting air flow?

The Lexus Automatic HVAC selects the mode based on ambient temperature and
the temp setting you dialed in. Warm ambient and cool setting should select the
dash level vents. Cold ambient with the same setting however will select only the
floor level flow, warm air rises, right?

I trust you have tapped the "Mode" button trying to get results, are you hearing any
mode doors moving, gently thumps or thuds?