When swapping the audio output device while running PIE or a packaged game on Windows, Quartz clocks stop. Does not repro in Release-4.27, but can be reproed in Release-5.0.
1) Sync to the AudioQA project
2) Launch the map AQ_Quartz
4) Enter the 0.1 Simple Test Clock - BPM test box
5) Observe a clapping sound plays at regular beats
6) Alt-tab out of PIE
7) In Windows, swap your Output Audio device to another device than the one you are currently using
8) Refocus the PIE window
The Quartz clock continues after you changing the audio output device (the regular claps are still heard)
The clock stops
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-150823 in the post.