Edit Record via URL is not working

Edit Record via URL is not working

According to the help page at https://help.creator.zoho.com/Editing-Records-via-Record-ID.html
the following format allows editing of a record via a URL:

http://creator.zoho.com/<userName>/<applinkname>/#Form:<formlinkname>?recLinkID=<recordID>&viewLinkName=<viewlinkname>

I've had this function working for months, but it seems now that I'm checking it that some of the records either don't appear fully (i.e. a blank screen) or some do work properly or inconsistently.

Here is a URL that should work, but doesn't:
https://creator.zoho.com/w21admin/w21data/#Form:Add_an_Event?recLinkID=340313000004455771&viewLinkName=Events

All of the parameters are correct.  But they don't work now.  Why?  

[Added]  I should note, you may click the link and wind up at the main application front door, but don't be deceived... it's supposed to take you to a form filled with data for editing. [/Added]

Please help.  My users depend on these URL-to-edit-record links to do their jobs.

As always, the application is shared with support.

Thank you for your quick assistance.