Lost unsynced changes

[GameDevIvan]

We just lost an unknown amount of unsynced changes in one CalDAV collection.
DAV5x is syncing with a Synology NAS (Synology Calendar app).
I noticed my partner's changes not syncing, so I took her phone and manually started a sync in DAV5x, which prompted for permissions (which is strange, since it had been working fine for years). After giving permissions and trying a sync again, I was shown the "at.bitfire.ical4android.InvalidCalendarException: Couldn't parse iCalendar" error and afterwards the one collection wasn't visible anymore in the "Business Calendar" app.
After updating DAV5x (installed via F-Droid), I was able to sync that collection again, but at that time, it had already been deleted from the phone (I presume from the Calendar Provider), with all of the unsynced changes, which are now lost.

How can I protect us from such data loss in the future?
The CalDAV collections are regularly backed up on the NAS, but the unsynced changes aren't backed up on the phones.
Is there a way to do backups of CalDAV collections on the phone?

I'm also disappointed, that there wasn't any error shown to the user after a prolonged period of not being able to sync (more than 2 weeks).

[devvv4ever]

Thanks for the report and sorry to hear that.

Normally errors like the mentioned one above get to be shown to the user instantly. However users may silence notifications and then they do not pop up again (we can't do anything against that...). After that maybe permissions got automatically removed. Android 11 has introduced the a "revoke permissions for apps" that are unused. So if the app couldn't sync anymore and notifications were silenced then Android maybe thought the app isn't used anymore and revoked the Calendar and Contacts permissions or either one of these.

An update should normally work without problems. Only if you remove the account then the unsynced collections are also removed from the app and from the system taking all unsynced changed with them. On some samsung devices there is an error not restoring system accounts like DAVx5 accounts are after a OS update.

To protect against a situation like this you can disable the "removing of permissions" in Android settings / Apps / DAVx⁵ / Permissons (disable "Remove permissions and free up space" option). Additionally if an error pops up send it to our support team (open a ticket on the website), and we'll try to resolve it. To prevent data loss of unsaved data you can use the app "iCal Import Export" and locally export the calendar. After setting DAVx5 up again you need to create a new empty calendar and import the calendar again into this empty collection and sync it up to the server. That is the only way to save unsynced data. Do not import the calendar data into the same existing calendar - it can cause duplicate entries then...

Hope that helps a bit.

[GameDevIvan]

I'm answering late due to vacations.
I've checked her device and the notifications weren't silenced. The Android OS version is 8.0.0
The DAVx5 acc was not wholly removed, as only one of the collections disappeared.
The app "iCal Import Export" doesn't seem to have any automatic export, so I can use it only in case of problems.
Thanks for your reply!

[devvv4ever]

Ohh Android 8.0.0 has sadly a weird caching bug... This is very rare and only occurs on Android 8.0.0 devices and maybe this is what you've been affected of.

https://www.davx5.com/faq/java-lang-nullpointerexception-java-util-gettimezone

The only thing we know is that it's related to system caches. You can uninstall DAVx⁵, then install it again and it should work again. Or alternatively you can update your Android version. It did not happen on any other Android version.

Yes at least if you notice a problem you can run the export tool once to be able to save unsynced changes. I don't know anything else I could recommend here...