Unfortunately, I do not know what is causing this error and am not able to replicate it. It has been showing up a couple times a day, on most days, under the store traffic we have on the site.
I notice that you must have cleared out our logs on the production site, and the error has not yet recurred. Did you make any other changes??
At any rate, I’ll watch for the error, and perhaps get some help from wpengine, our hosting company, to explore whether there might be a cacheing exclusion needed related to this problem.
Thanks again for your help trying to track this down.
Regards,
Ben