When we upgraded to Moodle 3.2 we found the following scenarios in the event monitoring subscription feature failing: "Receiving notification on site level" and "Receiving notification on course level".

I found that the failures were occurring because the changes made to the user notification preferences CSS selector in MDL-56299 assume that the (only/first) message output is the "Web"/popup output. We have more than one output that is available on install and so the popup notification preference is never set.

I solved the issue by using a more specific xpath selector.