5-month-old chickens losing feathers - molting or worse?

[Pretty Chickens]

They should not be going into any kind of heavy molt at this age. They do go through a juvenile molt but you should see new pin feathers growing in if that were the case.

I think the first thing I would do is spend some time watching your birds carefully and see if you have some aggressive or bully birds in your flock that have started pecking.

How much space is availlable to them in their coop/run? Do they free range or have access to pasture at all?

My chickens are free range. They go into their coops at night and I just close the doors. They sleep well all night. My room is very close to their coop and nothing disturbs them. The dogs watch them too. They don't peck and they are no aggressive.