One game is playing music, but not sound effects, when using my HDMI monitor's speakers

[granada777]

I have a Surface Book 2 laptop. It doesn't have video output, you're meant to use its general-purpose USB-C port to connect a USBC-to-HDMI adapter. Which I did.

I just got an HDMI monitor, Acer ET322QU, and connected it to my laptop. It has built-in speakers, which I was hoping to use.

I tried a couple of games I had installed and the speakers work fine.

But not Underrail. When I launch it:

a) At the native monitor resolution (2560x1440), with Windows configured to use monitor speakers: no audio at all
b) At native monitor resolution, using laptop speakers: everything works, music and sound effects
c) 1920x1080 resolution, monitor speakers: music works, sound effects don't
d) 1920x1080 resolution, laptop speakers : everything works

By sound effects I mean literally anything but the music, such as clicking a menu option, shooting a gun, etc.

(I also tried an Acer CB342CK with identical results so it's not just this monitor)

What could make a game behave differently depending on which speakers you use? It has no in-game audio options except volume sliders. I would have figured games would leave the audio playback to Windows.

I installed the latest monitor driver and the model is detected by Device Manager.

I'm not asking for help with this specific game, I'm trying to understand since I'm gonna use this external monitor from now one. If 1 game has this issue, it means I'll run into this issue again in some other future game.