I have two dashboards with custom drilldown search. One of them works just fine. But the other returns a blank page; looking into the SID I can see this error:
error:133 - Masking the original 404 message: 'Unexpected query string parameters: earliest, q, latest' with 'Page not found!' for security reasons
This actually happens to most custom drilldown searches that I try to set up, no matter which dashboard.
I use a CNAME for my server. If I change the URL to use the canonical name of the server, the "security" error goes away. Although this kind of makes sense, it doesn't explain why some custom searches do not trigger this problem. In the problematic dashboard, it fails even the simplest search like
sourcetype = this, i.e., no special character of any type.
I was seeing a similar error in trying to customize simple XML drilldown.
error:321 - Masking the original 404 message: 'Unexpected query string parameters: q' with 'Page not found!' for security reasons
Wasted a fair bit of time before finding this post. As OP says: seems broken in edit mode. Works after saving the dashboard.