At first it was happening once every dozen or so tactical missions, but as my game progressed, it became more frequent...
At start of tac missions, some soldiers have apparently randomly switched gear with another soldier. So stats, name, appearance is of one soldier, and gear and sometimes camouflage is from other soldier. I've had a look at console when it happens, didn't find anything unusual apart from one thing...when such soldier does a kill, it is credited to the owner of the gear.
Playing latest Muton's build.
Save-quit-load before mission when it happened sometimes helped, sometimes didn't. It mixes up again when restarting missions...