This doesn’t always happen, but happens very frequently.
When you’re in a Condo or a Lobby server and join another (perhaps without disconnecting from the menu), you connect to the server with your items “unequipped”. I still see my jetback in my hotbar, but I cannot use it until I reequip it.
All of my appearance items are equipped apparently, but none of them are actually shown.
Reconnecting server usually helps.