I have operated my BR 2 since 2018 without problems. I have now poor telemetry and spent many hours trying to solve this. I can not get telemetry to work with the tether. I installed a new Fathom x on topside and also new Fathom x in BR2. Not possible to ping 192.168.2.2. I have disconnected the tether and replaced it with a 2m long wire. It sometimes will respond when pinging but in most tests it will not respond at all. The response time on ping when it answers is average 7 ms. When I got telemetry the BR2 works fine. And it stays working for unlimited time without any lag in video.
Also replaced Rasberry Pi with a new SD card and flashed it with ardusub-rasbian.img. Pixhawk flashed to latest stable. When I connect network direct to network port on Pasberry Pi it always respond when pinging in less than 1ms.Network is set up according to your instructions. Firewall is disconnected and no antivirus.
Tested Tether on spool with Fathom-x at both ends and it reached a speed of 90 Mbps. Also replaced network cable betwen Rasberry Pi and Fathom-x in BR2. After that system seams to work again