AirPods refuse to hold connection, tried everything out there, including reset

So no matter the device (Mac, iPad or iPhone), my AirPods hold their bluetooth connection for between 20-50 seconds. Then the right one drops out, followed another 20-30 seconds by the left ear piece.

I have unpaired other devices (e.g. my Watch, which then created its own set of follow on issues), reset the AirPods (several times), turned off all AirPod functionality (Siri, in-ear sensing). I have literally tried everything I can find on the internet, and nothing has changed this behaviour.

Frustrating - they have not had massive amounts of use, are a few years old, and now virtually useless. I want to upgrade to the Pro version with NC, but I'm now hesitant given my experience.

Am I missing anything?

With thanks :)