Should never be on the latest OS for anything related to music. It's about stability and compatibility, and until they do something life changing like rewriting the audio driver structure so it's not an afterthought, any new MAC OS are solely about new and completely unrelated features to anything audio.
In most studios I've ever worked in, we used the oldest possible OS i.e. the iteration before it became functionally obsolete. Most are on Mavericks or Yosemite.
Don't sell a synth because the latest OS does't support it. Downgrade your OS.
Registered: Jan 2009
The most stable setup I ever had was Windows 7 and a 10 year old Fireface 400.