Thanks to yourself & all FP, FP community, and Google folk who helped resolve this; massively appreciated 
Quick question - before this was resolved, I’d used the below to disable Google Play Store:
I’ve now re-enabled that using adb shell pm enable com.android.vending, rebooted my device (not sure if required), and dragged my Google Play Store icon back onto my home screen (it was removed when the package was disabled).
I then opened Google Play Store, clicked on my profile image, selected Network Preferences, Auto-update apps, and put this back to Over Wi-Fi only (it had been Don't auto-update apps).
I then opened Google Play Store, clicked on my profile image, selected Manage apps and device > Manage > updates available and then selected and applied all pending updates.
Once all updates were applied, I rebooted again (for good measure). (All’s still good >1 hour after applying those updates).
Question: Are there any other actions that should be taken to put the phone back into it’s “normal” / non-workaround state. Thank-you again.