I often play with people online that can't put their diving suits on, but only the rebreather.
They have described the suit slot to be white when dragging the suit over (indicating it should go there) and simply nothing happens when they drag it over. We have tried restarting the game, server and suiciding ingame multiple times.
This occurs for all suits (We tried diving suits, pilot overalls and putting standard suits back on)
P.S. The classes are sufficient for the suits and i have been able to wear them myself as the same soldier.