Apple has released an unexpected iOS update. Version 12.3.1 was just released, without publishing or developing beta testing before that. It's unusual for Apple to fix an iOS update on a Friday, except in the case of critical, high-profile errors.
Fixing bugs is exactly what this release does. The official release notes for this update are brief:
Fixes an issue that can prevent you from receiving or receiving VoLTE calls.
Solves issues in Messages that can cause messages from unknown senders to appear in the call list, even though Filter Unknown Senders is enabled.
Fixes an issue that can prevent the error message from appearing in Messaging threads from unknown senders.
To update your iPhone or iPad, open the app Settings press General and then press Software Update .
If you have had trouble dialing, you may have been hit by the over-LTE error. The filtering and reporting error in Messaging also seems important, but none of these errors was widespread enough to attract national attention.
Why the unusual Friday solution? This is a great vacation weekend in the US, which is Monday's Memorial Day. It's a great weekend for travel, and many businesses are closed on Monday. Apple may have wanted to get it out before everyone leaves for the weekend, or maybe it would just be sure that the support staff have a chance to take Monday.