Hi Andrew,
thank for your quick answer. Yes, it affected a whole bunch of different mono sounds. I used a USB headset, so no problems with a headset jack, stereo sounds were played on both channels. The properties of the sounds looked like this:
Right click and play → Only at right channel instead of using both.
Here is the uasset file: (EDIT: Not allowed to upload this)
We had a presentation on friday where they only used only the left channel and linked them to both speakers. We could hear no footsteps and none of the other mono sounds which were played back with playSoundAtLocation().
I temporary fixed this upmixing all the sounds to pseudo-stereo (just copying the channel).