While sheep do fine with no "long fiber" and you must be feeding enough to keep them productive , I would think 2 things.
Boredom and habit. .Once they begin cribbing , or wool plucking ,they teach more and it never stop .
I question if your meeting the fiber needs. Particularly if limit feeding you hulls and cubes .
I see this in fat lambs on self feeders being fed limited rougah.
I now toss a pitch fork or 2 of rough or poor hay a day into feedlot lambs. Wood eating stopped.
If your limited feeding ewes,they will crib on anything. Your meeting thier calorie needs,but not thier FILL needs.
Hence why I feed free choice grass hay.
And make them clean up for a day,before another round bale added.