There's a crash on stadia when changing the audio device from 5.1 to stereo.
There's also a related issue where voice chat breaks when changing from 5.1 to stereo.
The background is that CL14889950 was introduced to fix a technical requirement violation for stadia in UE4.26+ and UE5. That CL appeared to worked well but there's a report from a licensee saying it causes a crash: [Link Removed]
The licensee kindly provided a fix and says that the issue needs to be fixed at the Mixer level, not the MixerPlatform level. This seems to require audio expertise to fix correctly.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-110447 in the post.