Hello,
Playing on US server 3664284. I am not able to switch hand items or weapons. I am able to do almost everything except intact with hands.

Log off and log back in.
Or press F5, that sometimes can fix hand bug.

If that doesn't work, then you might be triple carrying (2 guns on back, one in hands) and you don't have enough space for the third gun. You will need to temporarily drop one, and then use whatever you want and then pick it back up.