This has happened to me twice now. Can see the abilities on the bar flashing like I am clicking or pressing the button but nothing happens.
1st time was when I went to the quest where you destroy the possessed Woodsman’s Axe. put the axe in the pot and couldn’t attack anything when it started.
2nd time was in the Offal Pits in act 3 with Lorath for the “whispers of the Past” quest. As soon as I entered the Offal Pits none of my attacks or abilities worked again.
Had to leave game to the character select both times to fix. Seems to have something to do with entering a new area. Not sure if it is just dungeons and cellars or if it can trigger in open world too. I know leaving the area you just entered back to open world does not fix it.