Lately,on more populated servers using my inventory has been impossible. It won't allow me to do anything inventory wise ,except for opening up inventory screen, it won't allow me to pick up items in the world either, though when I exit and change servers changes I made when the inventory didn't work have saved to what I tried to modify it to.
For example, I'd find a vest on the ground, move my items into it and equip it, but when the inventory doesn't work my items won't move into the vest and the vest won't equip, and when I change server I'll have equipped the vest, and the items will be in the corresponding spaces.