Replacement Ring Doorbell Pro drops Wifi Connection Blue Circle is Continuous

Ring doorbell stopped working several weeks ago and got sent a replacement. Went through the setup process which successfully connected to my wifi ending with the usual "Rome wasn't built in a day" as it was checking for updates (I assume). The app says it has the latest firmware. History shows that some motion was logged. However it subsequently goes offline with the blue circle light circulating. And the app says its not connected to the wifi. BTW wifi signal is strong. (I have an ASUS RT-AC68U router that is 15ft away from the doorbell). A subsequent re-attempt (pressing the orange reset button) resulted in the same symptoms. The ASUS router log is showing the following:- Dec 20 05:04:06 syslog: wlceventd_proc_event(510): eth1: Auth **08:3A:88:24:6F:3F**, status: Successful (0) Dec 20 05:04:06 syslog: wlceventd_proc_event(539): eth1: Assoc 0**8:3A:88:24:6F:3F**, status: Successful (0) Dec 20 05:06:44 syslog: wlceventd_proc_event(474): eth1: Deauth_ind **08:3A:88:24:6F:3F**, status: 0, reason: Disassociated due to inactivity (4) Theory (1) - If the doorbell is attempting to check for firmware updates, and the website is not responding or taking a long time, would that explain why the wifi connection gets dropped by the router? Theory (2) - Could the replacement have the wrong website address for where to check for the firmware updates? Possible solution - disabling airtime fairness stop the router from dropping the wifi connection? (this wouldn't solve theory (2))