This has started to happen to me just in the last couple of days.
Never happened in the almost a year I have been playing then *boing* here it is; coincidentally or not, the same day I gain the ability to right click on the 1 & 2 slots and allow my weapons to auto-fire.
The alt-tabbing is only semi-effective and seems to gain me the ability to use the rest of the shortcut bar, but for some reason, not 1 & 2.
However when you bind this stuff to ALT, there doesn't seem to be any issue at all. vOv
Ground fighting is my favorite part of the game, so making it unplayable will be a show-stopper for me, sadly.
In a storyline mission near the end i could not use any skills.
I could walk, loot and holster my weapon and zoom but couldn´t shoot.
Alt+Tab didn´t help.
Adjust keybindings to shoot at a letter didn´t help.
Pressing a number marked my icon in the shortcut bar green for a bit of a second, but it did nothing.