I use Thunderbird to manage contacts and calendars. I use CardBook as vCard address book add-on and the default calendar. In order to sync everything with my phone, I set up a NextCloud account. Both contacts and events sync properly with my NextCloud account; I see all of them updated correctly in the web interface when making changes in my Thunderbird client.
However, some time last week, events stopped showing up in my Android calendar and in my Android contacts. I tried everything; I reset and checked correct permissions, including battery optimization. I re-installed the DAVx⁵ app from F-Droud. I made sure that the DAVx⁵ accounts show up in the system settings, with both “Address books” and “Calendar” option enabled in the “Account sync” menu.
Even if I execute a manual sync, nothing happens. No events show up in the calendar and the contacts are not updated in my address book. I use LineageOS without Google services on my Nexus 4a. The calendar is the built-in one (org.lineageos.etar). The contacts app is the default Android one (com.android.contacts).
Everything worked without any issues until recently. Was there an update that broke things? I didn’t change anything on my phone other than updating apps.