"Mudlumps" at base of feathers?

[MiddleChild]

My aging red star(?) hen had some problems last year that looked like she had a mild stroke. I held her up to eat and protected her from other hens and she came back, though she's still mopey and walks off center. Now she has a place on her upper back that she picks at and I thought the others were bugging her again. I looked tonight and she has lumps of what looks like mud hardened around the base of each feather. They're tan outside and grayish inside when broken. Each lump is about 1/4" long (along the feather rib) and about half that in diameter. Very hard; pulling them off takes the feather with it. Covers an area about 2" x 3". What on earth is this?

Middle Child

 

[sourland]

Are you certain that they are not mite or louse egg masses?

 

[Eggcessive]

Scroll down to lice in the link below to see if that is what you are seeing:
https://the-chicken-chick.com/poultry-lice-and-mites-identification/
Permethrin is a common spray or powder to use on chickens with lice at 10 day intervals until they are gone. The bedding should be removed, and the coop treated if that is what is happening. Pictures are always helpful.

 

[MiddleChild]

The lice-lump picture is close, but the lumps are smoother, with no egg-shapes visible. I'll assume that's what these are unless further information suggests otherwise. Many thanks!