If you haven’t launched Smite in a while, it may miss the fact that there are actually updates waiting for it, and just allow you to launch to the login screen, where you will receive a version mismatch after trying to sign in.
Here’s how to fix it:
Close smite if it’s still running, and then run the launcher again. While the launcher is open, run services.msc and stop and re-start the Hirez authentication and update service. Once the service has restarted, close the launcher and re-open it. It should now detect that there are updates.
Yes, I agree, this is a bit silly, but it works. 