Not a peep regarding issues with 2.0.4 at VersionTracker... 2.0.4 has been downloaded over 27,000 times via VersionTracker. One would expect myriad negative reviews if there was a significant bug in the software.
Google searches using the terms "Onyx 2.0.4," "Onyx 2.0.4 problem," and "Onyx 2.0.4 bug" returned no reports of problems on the first and second pages.
I suspect that your Apple tech experienced an isolated incident that may or may not have been caused by Onyx, but probably not...