You are using the GameProfile as the key to the backup graves lookup. GameProfile has both name and id as part of its hashCode. a player changing their name will cause their GameProfile to have a different hashCode and thus cause a different entry in the grave map. graves should be tracked by uuid which is unchanging in online-mode.

This change would cause no difference in offline mode as offline mode uuids are based on player name (offline mode name changes cause all player data to be lost, so this is a non-issue).