When attempting to navigate between my own created world and a friend's campaign world, I was able to navigate to the friend's world just fine by using the Switcher to switch to my character in their campaign. However, when I attempted to switch back to my own world, I was unable to do so using the elements of the World Anvil site. I was able to eventually get back to my world as the friend had a link to my own world, and I was able to use that to get back into editor mode for it.
After discussion in the World Anvil discord, it was discovered that the Switcher is not displaying all of the tabs that it should. Several tabs are also missing from the View Profile page. The only tabs viewable were HOME, Characters, Badges, and Guestbook (Screenshots can be provided upon request).
Other users unable to reproduce the bug, but I was able to reproduce it consistently. If need be, I would be willing to stream my session in a discord call to demonstrate the bug. Beyond that, steps unknown.
World Anvil switcher tabs
Profile Page tabs
This is happening because you have disabled the World Building features from your account.
You can go to the top right under "Features" and reactivate them to see what you are currently missing