I can only hear sound on one headset, why?
Some new systems are running with latest Intel processing technology.
In these specific cases, when you connect two Bluetooth headsets you might observe the second headset will have two different output devices in Windows device list, one from Intel and one from Microsoft driver, as you can see on the image below:
If you are in that case, you will have to select the one from Microsoft (with no "hardware acceleration" option). To do so, open the device properties and check: