I have spent a few hours trying to figure out which mod adds this and what it does...
I can upload a photo if needed but basically it looks like a red overheat bar that is on my kerbal during eva. The bar is always 75% full and always red.
It doesnt matter where the eva is, It can be on Kerbin, Burning up in the atmosphere, on the Mun... It's always there and always the same.
It's there on new games aswell so I think its some kind of feature from a mod and not a bug.
These are the mods I use: