[CLIENT/GAMEPLAY] Cannot sell in-game items

While playing on any game mode and any map, I can buy and use the UNDO button but** I'm unable to sell, the SELL button is always grey.** I can't use it anywhere in the shop area, either on the edge or deep inside. I've had this issue ever since I played on this account, I can't remember if I had it on any other ones, which means for at least a year. I never bothered to fix it until now and I've seen multiple unanswered bug reports on this board with the same issue.

The sell button being grey meaning it looks as if I weren't inside the shop area.

I have tried searching on google, probably clicked on 15 different links but found nothing helpful. I've tried reinstalling once and it hasn't changed.

My screen is not wierdly zoomed in and I can see the tab with the UNDO and SELL buttons. (two bugs I've read about on other posts)

Sorry for title, I'm not sure if it counts as client or gameplay.