[horde] iOS 13.2.1 and Reminders/Calendar Issues

[Cycle London]

Hi,
I have an issue with the Horde 'tasks' ('Nag', I believe?) and an iPhone
running iOS 13.2.1.  Either the latest iOS updates have broken something,
or else there is a problem with the Horde code.  I'm guessing the former.

The previous behaviour was that I could create an event or a reminder in
the Horde web interface, and it would almost immediately appear on my
mobile device.   Now, tasks created on the Horde do not appear on the
iPhone, and vice versa.   On the iPhone, if I go into 'Reminders' and tap
on 'Today', the screen stays blank for about a full minute, and then
displays every single task I have ever created, all marked as 'complete',
but all present nonetheless.  If I start to delete them, they reappear.

For the Calendar app, things are slightly different.   I open the app, the
events are there and then, within about ten seconds, they vanish.

As I write these words, I can't provide the sync log, as I'm in the office
so if that's needed, I can reply to that this evening.

I'm using Horde Groupware 5.2.22, Nag 4.2.19 and ActiveSync is the latest
version (updated on Saturday).

All help appreciated.