To clarify the fix with selecting another character first using Tocath's scenario:
Ezren gets his reward first, no problem. Before pressing the arrow to move on from the reward screen select another character. Not sure if you should select Valeros, another character or if that doesn't matter, but you have to do it before moving on to the screen where Valeros gets his reward.
Here's the thread were the workaround was first found and which has some more info: https://forums.obsidian.net/topic/86659-quest-mode-reward-bug/
Hope that helped.