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