At the moment, there's no way of knowing that a Zebra query failed unless you go into the Zebra server logs and have a certain level of verbosity for those logs. I'm proposing that we catch Zebra search errors and report them to the web server logs and surface them on the staff client. We can probably keep the OPAC the way it is as we probably don't want OPAC users seeing errors, but it could be good for staff to see, so that they can tell administrators and administrators can tell developers, and then we can fix all the things!
*** This bug has been marked as a duplicate of bug 27139 ***