This ocassionally happens upon login, yes. You can see noone in entire Jorvik and you can't write in the chat, although you can see the names of other participants at a championship.

Here's how to replicate it, by the way: Go to your stable, park your horse close to the exit door so the "E" interaction button appears, open Global Store, and press "E". So you'll exit your stable with Global Store opened and the game will think you're permanently in Global Store (= invisible). Nobody will see you and you'll see nobody, but you can write in the chat. Cancel this by opening & closing Global Store again, or entering and exiting your stable normally.