Hi I had the same problem.
Downgraded firmware back to 2.82 from 2.90 and all those IR's which I had dragged and dropped and then watched in disbelief as they disappeared from the editor, all of a sudden were there again under 2.82. I did not need to re-import them, they were there all of the time, just that the "new" firmware wasn't recognising them.
YMMV.
Hope this helps.