This is an Android bug that apparently happens after you install an app that can be your default SMS app.
To fix change your default SMS app to something else and then back to the SMS app you want to use.
If you’re using the Google Messages app you can make it refresh list all messages by
- swiping it away from the recents app list
- Sending another message with Join
That should make the app refresh itself. Check out a demo video here.
Unfortunately this is a bug in the Google Messages app that only Google can fix. Please contact their support so they are aware of the issue. Thanks!