Hello,
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
@devilkin I couldn’t reproduce the problem. (What is “a while”? A few days?) Which events must be in the calendar? Please provide more detailed steps to reproduce, so that I can reproduce the problem (for instance, which event do I have to create etc.). Does it only happen for events with specific characteristics or for all events?
Please provide debug info and verbose logs of a synchronization process where duplicate entries are created.
@rfc2822
It seems like all events on the calendar are duplicated at that point.
The only difference I saw was that it only happened to r/o calendars, not to the ones that FM is hosting for me directly. Also not all r/o calendars, but several.
Debug info: https://paste.fedoraproject.org/415184/
External log: http://www.kcore.org/tmp/davdroid-20239-20160827-150130.txt
Any idea what might be causing this? It keeps reoccurring. Might have to do with bad connectivity?
@devilkin said in Duplicate android entries on read-only calendars:
Any idea what might be causing this? It keeps reoccurring. Might have to do with bad connectivity?
Unfortunately, I don’t have any idea. Do you have any other clients (Thunderbird, …) to test? If the problem occurs for them, too, it’s probably a server problem.
I’m actually using Thunderbird too, and there the issue does not show up. Nor does it via a plugin for outlook 
EDIT: i installed another CalDav receiver (aCalDav - https://f-droid.org/repository/browse/?fdid=de.we.acaldav) next to yours on my phone. Seems to not trigger these issues.
I’d prefer to keep using yours, as it is a lot more refined, but right now, this bug is a showstopper for me.