I am in the Madracht fight, I just cast Mass Healing Word after selecting my entire party (4 members) and clicking confirm. All targets are in LOS, all conscious, and all have the Beacon of Hope buff.
The spell effect happened, but only one party member received healing, both on screen and in the combat log.
The game is now in a locked state where the spell is not finished. The bottom screen UI is gone. I can open menus, and they act as though it is still my turn (can't switch characters or perform any more interactions). I can not press space to end my turn.
Otherwise, the game is still responsive. I can move the camera, and click things, and the sounds/music still play.
That is all! Good luck :)
Edit: It just happened again with a normal Healing Word. The exact same thing, but only one target this time (obviously). Again with Beacon of Hope up. I will experiment a bit more with this!
Edit: I've reloaded this combat several times now, and it happens every time I heal someone who has the Beacon of Hope buff.