
Assuming this is the same bug we had on PC a couple months ago: It's a UI-related bug. On the server you are still regenerating stamina but the client performs a client-side check of your stamina before allowing a command to be sent to the server and because it thinks you don't have enough and aren't regenerating it will not allow you to use skills. You can perform a synchronizing action to get your client to properly update to match the server. The easiest and most common synchronizing actions is to simply light attack.
If it's not that bug, well then - Ouch.