Hi, happened to me 3 times (1 at NWAF, 2 in the South), only in firestation towers, only on 2nd or 3rd level. Last time yesterday, in Chernogorsk firestation, 3rd floor, when reached the top of the stairs.
I didn't die, instead all 3 times I got hit by an invisible ghost that ruined my shoes and my pants, and some objects inside took damage.
Only yesterday, it also made "My feet hurt" / "are sore", managed to cure it after morphine and painkillers.