Not a question... would like to report an issue with the API Explorer using the Sandbox environment. 'findItemsByCategory' does not return AspectHistogram information (no aspectHistogramContainer) is returned... however this element, along with related aspects, is returned when set to Production. Where does one report this type of issue? I've been running in circles for several hours and finally decided to try this in Production, and viola... there it is.
You can buy a technical support ticket and report the bug there. They will probably refund your payment after they acknowledge the bug. Someone on staff may eventually see this thread and note it internally. What you've discovered is pretty much known, however. The Finding API Sandbox isn't really kept up to par since using Production in our testing/coding is encouraged. (It would be nice if they posted noticed of the Finding API Sandbox's limitations more prominently.)