I too have been encountering this issue with bosses/goons having no problem lighting me up as a scav but spawned in pmc's dont insta brain me and act more like scavs themselves. You can even get them to follow you. If i brain one of these pmcs to the scavs will get angry and start shooting me even though they shoot these pmcs on sight.
The maps I have tested this on is customs and factory but mostly on factory.
I am also playing on server version SPT-AKI 3.2.5 with game version 12.12.32.19904
Just a few of the 260 users online
