For example, see https://test.wikipedia.org/wiki/User_talk:Roan_Kattouw_%28WMF%29 , which I deleted and restored. This has broken the alert flyout on testwiki for Catrope and Legoktm.
The error is PHP Fatal error: Call to a member function getText() on a non-object in /home/catrope/git/mediawiki/extensions/Echo/includes/formatters/MentionPresentationModel.php on line 51. This is because MentionPresentationModel doesn't take into account that $event->getTitle() can be null. EchoBasicFormatter::setTitleLink() deals with this by inserting a hideous [No page placeholder (T52829: Echo notifications should show the page name instead of [No page] if the page was deleted)
Change 249354 had a related patch set uploaded (by Catrope):
Comment out presentation model for mentions since it fatals on deleted pages
Change 249354 merged by jenkins-bot:
Comment out presentation model for mentions since it fatals on deleted pages
Change 249411 had a related patch set uploaded (by Legoktm):
Comment out presentation model for mentions since it fatals on deleted pages
Change 249411 merged by jenkins-bot:
Comment out presentation model for mentions since it fatals on deleted pages
Change 249444 had a related patch set uploaded (by Legoktm):
Allow presentation models to indicate a notification can't be formatted
Change 249444 merged by jenkins-bot:
Allow presentation models to indicate a notification can't be formatted
Checked in betalabs - no more BadMethodCallException.
The issue with [No page] as in T52829: Echo notifications should show the page name instead of [No page] if the page was deleted is still present. Clicking on notifications which refer to [No page], the deleted & restored page is perfectly displayed with all content.