So I reported this bug before but got completely ignored apparently.[Gameplay][Client?]
It's happened to me 6 or 7 times since I got the client update and it's still happening, but there's been no mention of it whatsoever in your client update bugs list or anything. It might not be the client but some kind of feedback should be given.
I'll report it again though sigh
Basically what happens is once you load into the game you can not use any hotkey abilities. Any buttons you press will not work, you can however click them. The only way to FIX this bug is to disconnect from the game and reconnect, wasting precious time getting back into the game. This happens randomly and there's no video or pictures I could give you since nothing changes visually, it's just that the buttons you press do not use abilities. I don't know how to reproduce it other than "load into the game and hope for the best".
It's a semi-rare occurance but it's pretty obnoxious and can single-handedly tip the game in the enemy's favor.