Is the current temps where you live quite low? I’ve had an older hen (6 years old) die when the first cold snap occurred. I should have been paying attention to temps, but she had fought hypothermia twice before, plus ailment for months which required tube feeding to get her through. She was absolutely fine throughout summer and fall, but it was the first night of freezing temps that killed her. She had just been through too much I think, and it weakened her systems.
The white bit of chicken’s poop are urates- essentially it’s pee, though chickens don’t pee like we do. Is any part of it yellow? That means infection. Is it greenish? That could be bile, meaning they aren’t eating enough, or no food is passing through. Diarrhea could mean pain- any panting?
You’ll have to describe more as to what “acting strange” means. That might give more clues. Have you felt for lumps and bumps? Any swelling? A dark blackish comb could be a heart issue, but couple that with liquidy expulsions with urates, I’m wondering if she was egg Bound? Did you see her straining?
