via specific steps you can obtain nothing in a floor of the tower

1. complete any floor except for a merchant floor
2. have an artifact on cooldown (recommended the time is as long as possible)
3. go to the doorway to the next floor
4. swap the cooldown artifact with a new one
5. the artifact has not been swapped but the game thinks it was (you can still go back)

this is a critical error that needs to be fixed as soon as possible