I've also had some issues with ical->diary times, but it's
a feature I've barely started using, so I don't have much
input and I'd not tried to debug it.

I'm using the mu4e email client as the UI for importing these
from email attachments, but AFAICS that's using icalendar.el
via: (icalendar-import-file path diary-file)

In my case the issue isn't restricted to recurring events,
and in general the times imported into the diary seem to be
0.5 hours later than they ought to be.  The example below
(full file attached) is for a meeting from 15:30 to 16:00
on the 20th, and it showed up in my diary as 16:00 to 16:30.

DTSTART;TZID=/freeassociation.sourceforge.net/Pacific/Auckland:
  20220620T153000
DTEND;TZID=/freeassociation.sourceforge.net/Pacific/Auckland:
  20220620T160000

Something noteworthy about the full attached file is just how
many entries there are for daylight savings vs standard time
within the VTIMEZONE block.  This seems to be a history of
daylight savings variations for the timezone, so I did wonder
whether that could be causing any confusion.


-Phil