Is it because you were hitting the attack button when the upgrade screen appeared?
Viewing post in Crystal Survivor jam comments
Fooled ya! There is no attack button.😁 The game auto attacks when enemies are near. Pressing the mouse or gamepad button during gameplay does nothing. You’re not the first to run into this. So this is clearly a failure on my part. As a player, how would you have liked to find out that the game features auto-attacking?