AirPods 4 disconnects from Apple Watch SE after 3s

My new AirPods 4 disconnect from my Apple Watch SE GPS 2nd Gen after around 3 seconds. I have: changed settings in the iPhone 15 so the AirPods don’t connect to the phone automatically, updated software on both phone and watch, unpaired and re-paired the AirPods, phone and watch but still the same issue. My watch has music downloaded and I don’t want to take my phone with me when walking. Infuriatingly, a £20 pair of JBL ear phones work seamlessly with the watch! Any suggestions would be very much appreciated.