My skin shows in the dressing room and on the main menu. It works fine in singleplayer.
Joining a server however gives me a random default skin. The “only show trusted skins” toggle is off.
This also happened during the office event but I assumed it was a bug with the server. I have started to think it might not be.
Custom skins are disabled in event servers. Which servers besides the event server are you experiencing this on?