Pokémon GO has resolved an issue that caused legacy level 41-50 avatar items to be incorrectly awarded to players who hadn’t reached the required levels before the recent level cap update. The affected items have now been removed from those accounts to maintain progression integrity. Players who earned the items legitimately will see no changes, while those impacted by the fix may notice the gear no longer in their inventory.
Source: Official Pokémon GO blog and Pokemon.com