Poor RSSI on Ring Video Doorbell (2nd Gen) with BT Smart Hub

I have had my Ring Video Doorbell (2nd Gen) and Chime for nearly a year, and have recently been seeing poor WiFi connectivity on the App. When checking device health the RSSI is between - 68 and -74

The first thing I tried was contacting my ISP (BT) who sent me a new BT Smart Hub (not the Smart Hub 2), but that did not solve the problem.

I then contacted Ring Tech Support, who have been brilliant. These are the troubleshooting things we have tried together:

Changing the 2gHz channel on the (new) router from 11 to 1, or 6 - didn’t work
Moving the router closer to the doorbell - didn’t work, although I am limited by the length of my ethernet cable, and where the line comes into the house. The router is approx 3 meters away from the doorbell
Doing a speed Bandwidth Place speed test (recommended by Ring ) near the doorbell - speeds all well above the recommended speeds for the device
Trying a TP-Link AC750 WiFi Extender/Booster - didn’t work
Trying a new Ring Chime Pro - didn’t work
Trying a brand new replacement Ring Video Doorbell (2nd Gen) - didn’t work.

When I bring the Doorbell indoors and place it next to the router, the RSSI is in the -40s

When I move it one to two meters away from the router, it is in the -50s

Ring (after all their help) have suggested I contact my ISP (BT), but looking at their website, I have the most up-to-date router available from them.

Does anyone have any other ideas please. I am in the UK

A BT engineer has been today and has done lots of testing on the BT Smart Hub router which, as suspected, is correctly positioned and close to the Ring doorbell, and working as it should. The engineer also replaced the wall socket and the broadband cable to the router. (Which are both only 9 years old), but this made no difference either. My speed tests were all excellent too.

This is the interesting bit though. The BT engineer said that they are seeing lots of BT customers who have Ring doorbells who are having the same issue.

Is there some sort of incompatibility between Ring devices and BT routers, does anyone know?

BT is one of the leading ISPs in the UK. Surely Ring should be fully compatible with BT routers?