This is the Happy Wars Management Team.
With the release of the Boss Mission, we encountered the following issue:
If the season changes while you still have Monster Slayer in a Buff Gem, it will change into another buff and an empty Buff Gem will remain in the inventory.
An empty Buff Gem cannot be removed from the inventory, so please remove Monster Slayer from the Buff Gem in Item Remodeling before the season changes.
This issue will be fixed in the next update.
We apologize for any inconvenience this may have caused.
Issue regarding empty Buff Gems