Bluetooth controls not working any more (Windows 10 + Shokz OpenMove Headset)?

Hello,

Sometimes the controls on my Shokz OpenMove headset stop working with my Windows 10 PC.

I'm playing a video on YouTube and then walking around the apartment (doing chores).

Normally, I can easily adjust the volume (+/-) or pause/play when needed.

But sometimes it doesn't work. When I press the play/pause button, I only get a "beep" sound (but it doesn't affect playback), and when I press the (+/-) buttons, I get a "battery medium" message... but nothing happens.

It can't be a reception issue because the problem persists even when I'm standing right next to my notebook.

What could be causing this, and how can I troubleshoot and fix it?
I've the feeling that it is now not working any more at all.

Windows 10 Pro 22H2 (OS Build 19045.6466)