I’ve been using nextcloud for some time now as my main calendar, but I noticed some syncing issues on iOS and ipadOS devices.
Some info of my setup:
OS: Unraid with nextcloud running in a docker container
nextcloud version: 27.0.0 (issue is also present on versions 23 and newer)
I currently have an android phone running dav5x connected to the calendar (no issues there).
When an iOS device has been connected to it for some time I start to see syncing issues (calendar event changes not showing up, in rare cases this also extend to tasks).
The solution is to disable and enable the calendar link switch in the accounts setting in iOS, but that doesn’t feel like a good solution.
I think the problem is with the push setting in iOS (where data is pushed from the server to the client device when possible). The server is available 24/7 with the usual container updates, but I don’t think those updates are the cause of the sync issues. My money would be on a server config issue or bug in nextcloud that causes them.