Apparently the AudioMixer has a (now resolved) bug where upon selection it will freeze the entire editor. On update we experienced this issue and we reverted back to an older working version of Unity (5.4.1p3).
The issue is marked as resolved for 5.6.0 Unity Issue Tracker - Unity Editor freezes when attempting to open a .mixer asset in the Audio Mixer Window
However, given how fundamental an issue it is and how many versions it affects, it would be somewhat surprising for the answer to essentially be “Skip the 5.5 cycle if you want to use the AudioMixer to be stable”. So is there any information on whether or not the fix will be applied in upcoming patch releases of 5.4 or even 5.5?
Given some of the constraints we work with (recommended/supported versions by hardware vendors) waiting for 5.6 is not an option and would mean having to develop our own audio solution.