I’ve recently subscribed to fastmail, and I was looking to start using their calendar (caldav) service too.
Configured it in DavDroid (f-droid version for now), fairly straightforward, and it started syncing fine to my Android calendar (on Marshmallow, OnePlus3)
On Fastmail I have a few calendars of my own, and a few I pull in from various sources. These always display fine on FM - no duplicate entires or anything…
After a few days I started noticing duplicate entries in these calendars, some double, some triple, this morning quadruple.
Removing the calendar from sync in DavDroid, refreshing the Android calendar, and then re-adding them makes the problem go away… for a little while. I’ve already seen duplicate entries again on one of my calendars.
Steps to reproduce: remove account, readd account, after a while they pop up duplicate/triplicate again