I’ve had this occur twice, typically around 7 to 8 PM after arriving home from work.
Because it happens sporadically, I may have the events slightly confused but to my recollection:
First instance: Noticing I hadn’t received any messages for a about an hour, I saw I had lost cell connection. I did as @Jose_Briones often describes and reset the SIM connection. This is a common thing to do on Pure (though less so with the new update) and can be performed a number of ways: The hardware slider, switching between SIMS1 and 2, etc.
This didn’t work this time So I checked to see if my default APN had changed (I have gotten better signal performance by adding a manual APN as per my MVNO). Going into APN settings, every entry—my custom and the automatic— had vanished.
Worried, I readded my MVNO’s suggested APN. After a few seconds 12 texts came rolling in and all the APN entries repopulated: including the original AND new, duplicate MVNO access point I entered. I deleted the duplicate and everything was fine.
In the Second instance, last night, the same thing happened,. I did the same sequence of testing, but after re-adding my access point, the list did not repopulate and I did not reconnect. Restarting the device reconnected me, and repopulated the APN settings list—again with my duplicate.