The campaign file is in the HU folder save/game and has the filename .csf_bin , if you want to test if this is the problem, put it in a zip file and delete the original temporarily.
I think the files are faulty with you here are the originals https://gist.github.com/drguildo/eacd4018bb327d486c29 note the filename c_unlockedhero.xml which is wrong here in the example c_unlockedheroes.xml
The same happened to me several years ago for Jodit Haile, a DS specialist.
She always appeared as KIA in Quick Missions.
Maybe a carryover from the campaign where she was unlocked but later died?
I'm guessing it is in the campaign save file which name escapes me now.
Don't know if you still lurk around, but here are my 2 cents:
Play HU with its optional "Legacy" add-on. It rolls the louadout craziness back to around the default game. That is, 16 or so sets for each soldier (and most have some sort of magnification).
Also, I'm playing on Realistic option (the middle difficulty level of HU) and I find Support useful in certain missions to spread suppressive fire in the overall enemy position.
And last but not least: I found out stealth makes a significant difference in the enemy detecting you. So I suggest avoiding Support operators for most missions, as they're the loudest ones, and going predominantly Rifleman+Demo+Snipers. One satisfying mode of play I like is taking the Sniper role and coordnate the other fireteams from afar, covering them as needed.
Hope it helps. Cheers.