Sometimes if you take one of these into a mission and don't use it then it will be in your pack but their is no option to use it anymore in future missions. Tried dropping/picking up with same or different character, and another taking it from your pack. Nevers shows as option to use it in tactical menu. Tried putting into stash, playing a mission, then trying to use it a a 3rd mission and still might not be usable.
I assume most people keep them in the pack and use it it the last round. AI seem to gang up hard if you use before. Might be better to automatically apply these at the beginning of the mission w/o cost but have some less debuff. Would make them play more as intended and prevent overuse.