I'm sure there is no problem, but most have lots copious amounts of weight and there probably won't be much muscle left on the carcass. I don't eat my hens anyway so it was never an issue.
It's hard to say about the pain. Chickens are very stoic animals. Unless you press on the abdomen and they bite at your arm a little or struggle, you wouldn't know. Most likely, unless a mass is pressing on nerves, they probably are not in a lot of pain with some of this. Wish we could ask them...
This one appears to be reproductive cancer to me, the nodules all over. My 5 yr old RIR hatchery hen looked very much like that inside when she passed away.
The second one, I'm not entirely sure what I'm looking at. I see a lump that if you cut it open, might be indicative of internal laying...