[solved] Since migration, Thunderbird is unable to sync calendars

I have recently migrated a Nextcloud installation from a server running apache to one running Nginx, which went mostly smoothly.

Thunderbird / Lightning is however unable to sync, immediately after setting up a calendar, warning signs appear next to it. In the thunderbird error console I read:

Timestamp: 03/24/17 15:51:31
Warning: There has been an error reading data for calendar: Johannes. However, this error is believed to be minor, so the program will attempt to continue. Error code: DAV_NOT_DAV. Description: The resource at https://owncloud.rohr.org/remote.php/dav/calendars/jr/defaultcalendar/ is either not a DAV collection or not available
Source File: file:///home/jr/.thunderbird/default/ag1kqdiz.slt/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D/calendar-js/calCalendarManager.js
Line: 962
Timestamp: 03/24/17 15:51:31
Warning: There has been an error reading data for calendar: Johannes. However, this error is believed to be minor, so the program will attempt to continue. Error code: READ_FAILED. Description:
Source File: file:///home/jr/.thunderbird/default/ag1kqdiz.slt/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D/calendar-js/calCalendarManager.js
Line: 962

Timestamp: 03/24/17 15:51:31
Error: [calCachedCalendar] replay action failed: null, uri=https://owncloud.rohr.org/remote.php/dav/calendars/jr/defaultcalendar/, result=2147500037, op=[xpconnect wrapped calIOperation]
Source File: file:///home/jr/.thunderbird/default/ag1kqdiz.slt/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D/calendar-js/calCachedCalendar.js
Line: 327

Timestamp: 03/24/17 15:51:32
Error: Error Parsing ICS: 2152333568
Source File: file:///home/jr/.thunderbird/default/ag1kqdiz.slt/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D/calendar-js/calIcsParser.js
Line: 136
Timestamp: 03/24/17 15:52:22
Error: uncaught exception: 2147746065
Source File: resource:///modules/activity/autosync.js
Line: 210

there are no related log entries in nextcloud.log, last entry is already 2 hours old and I can’t even see entries in the Nginx access log, as if the connection already fails at an earlier stage, before Tbird sends a request.

Does anyone have a suggestion what might be going on here? For reference, I have put the ngix vserver config here: https://gist.github.com/vasyugan/6455fa5d7c6bcdc9c413944adb248bc4

Thank you very much in advance!

The solution is here: Thunderbird-Lightening-Cardbook Caldav & Carddav broken after upgrade to Nextcloud 11