Hi cmn,
The sandbox feature has been rolling out to the various clusters over the last few days. If you are having any troubles with sandbox you can send us any error information and we can either share any work arounds or author fixes.
There are a few steps that can be taken for debugging and testing. A lot of it depends on the nature of what is "not working". If the visual is not rendering anything at all that would be different than a visual which is rendering but not reacting properly to a mouse event for example. The first thing I always look for are errors in the browser console log. If there are any error messages there or stack traces that can help identify any issues.
Can you please elaborate in more detail what is not working?
Thanks,
Bashir