Ok, the fix was actually pretty simple. You were right about the deform, I just had to re enable it for all bones before manipulating the mesh.
Most of the feathers I hadn’t gotten around to – just the three closest to the body!
They are working now, though the tertiary (top) feather layer isn’t moving along. I suspect it has something to do with these vertex groups only including the primary and secondary layer. Thanks for the troubleshooting!

