Door bell notifications on phone

I have a Peephole doorbell and am using the Android app on 2 Google Pixel phones - A Pixel 3 with the primary ring account that the bell is registered to - A Pixel 3a with an account the bell is shared with Both phones are configured with exactly the same settings and tones. Both phones notify of movement, however quite often the phone on the primary account does not receive notification that the button has been pushed and play the tone whereas the phone on the shared account always works. This means that we have missed people ringing the doorbell, not great for a doorbell seeing as it is it's primary purpose. Obviously the event is recorded in the history (not surprising as it notified one of the phones correctly) so the issue is not with the bell but with the way the app is being notified or processing the notification. I have checked all the permissions and battery saving modes on both phones and they are identical with no restrictions or optimising switched on. Also both phones have the same number of limited apps on them (as I manage both phones).