Thrown when something has gone wrong with Device Sync in a way that is not recoverable.
Generally, errors of this kind are due to incompatible versions of Realm and Atlas App Services being used or bugs in the library or on the server, and the only fix would be installing a new version of the app with a new version of Realm.
It is still possible to use the Realm locally after this error occurs. However, this must be done with caution as data written to the realm after this point risk getting lost as many errors of this category will result in a Client Reset once the client re-connects to the server.
which is responsible for handling this type of exceptions.