... and even should not have been sent me because I didn't recieve any notifications during Friday (on Wikidata).
The message is a summary (the option "A daily summary of notifications" was selected in Preferences-Notificaitons.
The email of daily summary notifications has more details than the screenshot in the ticket.
It might be that details about the type of messages and the page(s) from where messages come are omitted when types of messages are quite different or/and messages come from different pages.
Sorry, I misunderstood. I somehow missed the fact that the email was empty.
If none of the notifications can be rendered (canRender() returns false) then an empty email would likely be sent. I'll fix that and check for other cases.