Notifications don't show any content on iOS

[gnunicorn]

On iOS when installed properly (see docs) the Notifications arrive at the Background Service. More often than not that seems to be unable to fetch all the content of the event so we can display it -- whether that is due to a lack of time or resources isn't clear. We might want to consider adding capability to trace some of that (unclear if feasible). However, it is most likely due to us not yet using simplified sliding sync and can't be fixed before we support simplified sliding sync...