This bug happened to me twice today.

When collecting a reward from Klaas, instead of the screen dimming and telling you what reward you've obtained, that screen was instantly skipped. The message "Klaas gave you a Treasure Chest!" appeared, but the rewards were not stated. As I did not take note of my potions and tokens, I'm unsure if I did receive a reward because there were no new elixirs or eggs.

Edit: I did not press anything or click anything to make that screen go away.