One Sided
This looks a bit like a waiter walking toward you with a platter in their hands... but wait. It's only half of a waiter. It's a one sided waiter!
An update is needed before you can continue but you have more than one WaniKani tab open.
Finish up what ever you are doing on the other tab(s), then close them to continue.
The update will complete automatically once the other tab(s) are closed.