Why does my cosmetic appear restricted or change to default in some Fortnite islands?

While there are thousands of Fortnite cosmetics available for all experiences, a small portion are not compatible with E or E10+ (or regionally equivalent) game ratings. In these cases, players will notice an icon in their Locker and in the Item Shop indicating which cosmetics cannot be equipped inside islands below a certain ratings threshold.

If a player equips one of these items and joins an island below the designated rating threshold, their equipped item will appear as an item that’s compatible with the island’s rating. (For example, their Outfit will appear as a default Outfit.)

You can find detailed information here: Island Age Ratings Now in Fortnite! (Opens in a new tab)