@Fabien_: Sorry to hear that you're having these issues. Have you tried connecting the J6+ to other Bluetooth compatible devices to see if you experience similar issues? Are you making sure to stay within range of the phone while connected (around 10m)?
From a troubleshooting standpoint, I feel like you've tried most of the following, but please restart your phone and check that the phone's software is up to date by going to Settings > Software Update. Furthermore please go to Settings > Connections > Bluetooth and ensure that it is enabled. Then, make your headphones visible by following the manufacturers instructions, select them from the list of available devices, enter a PIN if prompted and you should be good to go.
If the issue persists then head into Settings > Apps > 3 dots (top right) > Show System Apps > Bluetooth Share / Bluetooth Test > Storage > Clear cache / data. If this doesn't help, go into your Bluetooth settings, select the device you are having problems with and then tap "Forget" or “Unpair” from that device and then restart your phone. If the problem persists then run the hardware test: Samsung Members app > Get Help > Interactive Checks > Run through the Bluetooth test and share the results. Let me know how you get on.
From a troubleshooting standpoint, I feel like you've tried most of the following, but please restart your phone and check that the phone's software is up to date by going to Settings > Software Update. Furthermore please go to Settings > Connections > Bluetooth and ensure that it is enabled. Then, make your headphones visible by following the manufacturers instructions, select them from the list of available devices, enter a PIN if prompted and you should be good to go.
If the issue persists then head into Settings > Apps > 3 dots (top right) > Show System Apps > Bluetooth Share / Bluetooth Test > Storage > Clear cache / data. If this doesn't help, go into your Bluetooth settings, select the device you are having problems with and then tap "Forget" or “Unpair” from that device and then restart your phone. If the problem persists then run the hardware test: Samsung Members app > Get Help > Interactive Checks > Run through the Bluetooth test and share the results. Let me know how you get on.
