This is a bug that occurs when you attempt to load a saved game. A solider will randomly change into different armor and the original armor is just gone.
Is this bug being worked on? And how about an ETA for a hotfix?
While not totally gamebreaking it does cause lots of grief since it eats away at your resources when you can not deploy your team cause your soliders have no weapons or armor
Your save game being infected by panda virus, it transform into nikid soldier! 
ruuuunnn!
Anyway you can see the devs progress for upcoming patch thru canny > https://phoenixpoint.canny.io/feedback?status=in-progress
This is a bug that was supposedly fixed in the last Backer Build and re-introduced in either the final release or an early patch. I do not see this bug in the Feedback Tool. So, there is no means to track it.