I started having this problem after switching from AT&T to Google Fi about a year ago. I found a few posts where people said to download the Google Messages app, tap the three dots to get into settings, select Chat Features and turn this off. I updated my apps from Play store, than I went back to the Google Messages app and at the bottom of the screen it ...
I got on chat with Google FI Support who walked me through through these fixes.
Goto Settings>Apps>GoogleFi>Storage and tap Clear Data
Open Google FI app and complete setup.
If this recurs make sure to contact support to make sure your network is fixed.