7.1 Sound missing two channels

When testing our game with a 7.1 system we encountered a strange issue that caused two channels to not work at all. Whenever the sound origin is exactly 90° in either direction it’s almost silent.

We are spawning in the Audio via Blueprint with “Spawn Sound at Location”.

I’m aware that a similar issue existed before 4.4 and was supposedly fixed.

I also took a look at the documentation which describes how to import files with surround sound support by providing wav files with specific endings in the file name. But that surely isn’t necessary when we want a simple sound placed in the level to be played on all channels is it?

Are we just overlooking something obvious (the first time really diving into audio with unreal engine for the whole team) or is this another bug?