I have 'next weapon' binded to my shift key. Quite a few times during missions I all of a sudden find myself not able to switch with the shift button (yes i have ammo in all weapons, more then one weapon), so I have to select the weapon using the number keys. Then out of nowhere it seems to work with shift again, then not. Its weird.

Have you hit any of the keys like I, O, or P?  Maybe it's I, O, U, but that allows for best safe/unsafe weapons ect.   I've done the same thing...that'll teach me to pay attention

It sounds like you might have your weapon switching mode set to "best safe weapon" or "best weapon". If you're still having this problem would you please try setting your weapon switching mode to "normal" (there's a key bound to it as defined in the "control settings" menu...look for "normal weapon switching") and post the results.

I have the same problem, sometimes it works and sometimes it doesn't and it has nothing to do with best safe weapon best unsafe weapon buttons. Other than that I've had no "bugs".

Have you tried hitting 'U', or what ever you have normal weapons switching bound to?  I was disbelieving that and having same problem, and I hit u, and my switching problem was fixed.