I was trying to get my JBL Flip 4 waterproof speakers (2) to work in stereo on my X280. I could get them to pair, but Windows 10 would only output to 1 speaker. Some googleing and I found the solution. Install Voice Meeter. See the last post in the following thread where I found the solution. I connected both speakers in Windows using bluetooth, but without pressing the linking buttons on the speakers (the button below the power button). Next I just had to choose the hardware out devices in the Voice Meeter app. Voila!
Bluetooth Speakers - listen to 2 at the same time???
EDIT: I thought I was getting stereo because the mono button on Voice Meeter did change the sound, but on further experimentation, I realize both speakers are essentially putting out the same sound. It sounds quite good, the sound coming out of 2 speakers, but it is not stereo.
It might be a bluetooth driver issue.