I think the problem has resolved itself without the need for a reset - which I was going to try today before I ended up painting a fence instead.
Basically I signed out and deinstalled everything on the iPhone (where the beta was installed) as described on Monday/Tuesday and reset the alerts.
I then reinstalled the standard app and disabled/enabled the alerts. I noticed that the scan time had changed to 2 or 3 times a second so I reset back to my preference of every 5 seconds. Progress - no alerts at all yesterday.
Then I remembered I have the app on the iPad and signed out ad back in on that. The scan settings were fine at 5 seconds.
Today, the alerts seem to be arriving normally and the door functions and reports its status just fine.
I haven't reinstalled the beta yet but my thinking is that something set the scan periods to the default and life got confused across the 3 iOS apps. Interestingly, I think the iPad was ok all along but I rarely use the app to check on the door, much less to operate it.
I haven't reset or powered off the garadget unit so software conflict looks the likely cause.