from time to time the game glitches and its not possible to 'talk' to certain characters in order to do their quest,

this example is Barcus on the windmill the steps to reproduce it are ;
1 press the break to stop the windmill turning
2 during the fight against the golbins set of a bomb or spell effect that damages the windmile parts... doing this restarts the windmill as was part of the quest but if was changed by Larian and because the windmill is now damaged you can't stop it turning again... it actually does not turn but the animation plays and you can't talk to Barus [see image Barcus1]

workaround / repair

fast travel to any location like the village stone then you should be able to talk to Barcus in order to free him [see image Barcus2]