C2422HE, MST, P2422H, audio problems

I got several workplaces which has a combination of a C2422HE and a P2422H monitor, connected between each other with a DP cable.

The user connects a HP Probook laptop to the C2422HE monitor with a USB Type-C cable. That way they have a dual monitor workplace with everything going to the USB Type-C connection.

This works great, except that it's giving audio issues for some users. We mainly use the HP Probook 450 G8 series and the HP Probook x360 series. The audio problem only seems to be occuring with the 450 G8 series laptops.
I've seen it happening for at least two users, using the same model laptop. For one user, it helps to use the audio troubleshooting function in Windows 10, the audio works through the monitor as soon as it gives the option to disable spatial sound. But the audio cuts out again as soon as the volume is adjusted through the controls on the soundbar or when the laptop is reconnected to the monitor. For the other uses, I haven't found a workaround yet for this problem.

I checked the audio devices set in Windows, it's for both correctly set to the audio device from the monitor.
I also tried updating the firmware, which was succesful, but didn't solve the problem.

Does anyone know what can cause this issue and how to fix it?