After getting some interesting, unexpected, and slightly exasperating outcomes with the certificate module in Moodle 1.9+ when using linked activity option, I decided to do a little testing.
Typically, we have multiple activities in our workshops and each activity is graded using a Scale (in our case - unsat/sat). Participants must complete each activity satisfactorily in order to download certificate. I set the certificate using Linked Activity option and set the activity for a required grade of 100% (a "sat" grade on the scale for the activity). Sometimes this works and sometimes it doesn't. When it doesn't the typical outcome is usually a blank screen when clicking on the certificate link from the home page. See this certificate testing video to see what I've done so far.
(note - Often, the person in the teacher role will be able to see/download a certificate even when people in the student role can't so make sure to use student test accounts for this.)
Since the blank screen outcome seemed random, I began methodically testing various circumstances to discover if there was some sort of pattern to the madness. My testing isn't complete (there are hundreds if not thousands of permutations!) but patterns do seem to be emerging.
You can view the results of my tests so far by going to my gdoc spreadsheet. You don't need a google account to view this.
If you'd like to help me test these things out. I have created a form to easily collect your data. Feel free to use this form to add your testing data.
I look forward to reading about your results or your experiences with the certificate module.