So sorry for your losses. I know how frustrating this must be!

Try see if you can find an "all-flock" feed for them. That's usually 20% protein. The hens will need oyster shell in a separate feeder/dish as it's lower in calcium.
I know you said they have plenty of room, but just in case, I'm putting this here so you can check, as maybe it's not enough. Chickens need a minimum of 4 square feet of clear floor space in a coop and 15 square feet in a run. I'm sorry for sounding morbid here, but now with less chickens I'd think this should help if it had
anything at all to due with overcrowding.
Any chance you could pick up a camera that works at night too? Just in case something else is doing this, plus, if it's a particular chicken or chickens doing it, you could pull them out and separate for a while and we'll try help you with the next move from there.