Skin Shown As Default Steve To My Friend

I made a snapshot server (21w05b) on Java Minecraft with my friend. Everything works perfectly except for where my friend only sees my skin as the default steve skin. In my perspective I can see my custom skin, including my friend's custom skin. I've tried re-logging and changing skins and we still have the same problem. It's been the same for a couple of days and hasn't happened on our other servers.