@3KillerBs has covered it more than adequately.
The Nutrena Layer feed is fine for what it is, but it is designed to meet dietary minimums of commercial layers in commercial mangement settings, at the lowest possible cost, not for the long term health of the bird. Scratch, typically, is 8-9% protein, which drags protein levels down from that minimum number VERY rapidly. Your BSFL (TY! for linking the nutrition label), if you treat it as a treat (not more than 10% of the diet, by weight, daily) adds about 3.5% to your chicken's daily protein intake (and its a complete protein, that's good). Chickens, particularly dual purpose birds, or birds in holt, or young birds before start of lay, perform better at protein levels between 18-20%. Unfortunately, the BSFL also bring a LOT of fat.
The target fat level for a chicken's diet is about 3.5% +/-. Nutrena's NatureWise 16% Layer is 2.5% fat. adding the 10% (by weight) BSFL to their feed brings that fat level up from 2.5% to 6.0%! That's a level used for fattening CornishX for table, and not much else.
Even so, while feather picking CAN be a sign of protein deficiency (and may be, in your flock, depending on how much scratch they get), the BSFL, plus the self-picking, plus the lack of similar behaviors from other birds leads me to suspect some other cause.
I would, on general principles, recommend a return to just the commercial feed for a 2 week period - no treats - or even a brief substitution with a small bag of all flock or starter-grower to bump up the protein level - or even Nutrena's "feather fixer", which is simply a higher protein (18%) "layer feed" - just in case this is an artifact of the increased protein needs of molt. Maybe it resolves the issue.
It can also be neurological/pure boredom. They look like they have plenty of room, but you could add some clutter.
and yes, definite bug check.
