I'm not sure what could be causing this. We've fixed several problems related to audio preferences recently.
We'd appreciate if you could tell when and where(from the dashboard or from inside a project) you change your output setting and where/when you notice that it reverts to the default output.
And also if you could quit the application just after the output goes back to defaut and send us ohm studio's log files. There's an application called ohm studio beta reporter that serves this purpose.