The image for the Hero Level 5 chest appears as a white square in the Victory screen for Yrel, as seen in the screenshot below:
imgur (dot) com/a/KyQ3FH1
Also happens in the Play’s Change Hero screen when you hover over the exclamation icon.
Reach Hero Level 5 (white square instead of a chest).
imgur (dot) com/a/DQeIdhB
The Hero Progression reward tooltip also says:
- (empty)
- 500 gold