I managed to get them working, following the advice from Jabra - which is broadly similar to advice given but here’s the full techniii followed:
Thank you for contacting Jabra Support. To address the challenge you have described with your Jabra Elite 8 Active, please follow these steps:
Reset your earbuds:
Go to the Bluetooth menu on your mobile device and unpair your earbuds by selecting Unpair/Forget this Device (or similar).
Turn off the Bluetooth setting on your mobile device.
Turn your mobile device off and then on again.
Place both earbuds in the charging case and leave the lid open. Ensure your earbuds are sufficiently charged.
Press and hold (10 seconds) the Left and Right buttons on the earbuds simultaneously until the LED on the inside of the charging case flashes pink.
Close the lid of the charging case (5 seconds) to complete the reset.
Note: You cannot reset only one of the earbuds.
Turn on the Bluetooth setting on your mobile device.
Remove the earbuds from the case and re-pair them to your mobile device by selecting the Jabra Elite 8 Active from the list of available devices in the Bluetooth menu.
Update or re-install the firmware:
You will need to use the Jabra Sound+ app. You can download it for free here:
Jabra Sound+ - Android
Jabra Sound+ - iOS
Make sure your earbuds are paired with your mobile device and have at least 50% battery.
Open Jabra Sound+ and make sure the earbuds are detected (they will be displayed by the Jabra device name as yellow circles with an L and R and may take a few minutes to appear).
From the main headset tab, click on the Settings icon in the top right corner.
If there is a new firmware version available, select Firmware update available.
If there is no new firmware version available, select Personalize your headset, then Voice guidance language. Re-select the current language of the earbuds.
Tap Update Now and follow the onscreen instructions to complete the update.
NOTE: Do not open the charging case until at least 10 seconds after it has stopped flashing pink. If the LED does not stop flashing after 15 minutes, open the lid of the charging case and close it again.
If an error occurs during the firmware update, the LED on the charging case will flash red. To restart the firmware update, make sure the charging case is connected to a power supply, remove the earbuds from the charging case and then place the earbuds back in the charging case and close the lid.