Calendar and contact synchronisation with Thunderbird broken after migration to Nextcloud 12.0.0 #5092

Steps to reproduce

I successfully migrated from Nextcloud 11.0.2 to 12.0.0 (on 3 different instances).
To see my calendars and contacts on my laptop running OS X 10.11.6, I am using Thunderbird 51.1.1 using Lightning 5.4.1.1 and Inverse SOGo Connector 31.0.0.

Expected behaviour

Calendars and contacts synchronisation should work.

Actual behaviour

Calendars and contacts synchronisation does not happened any more, on any of the 3 instances.

Server configuration

Operating system: Linux

Web server: Apache

Database: PostgreSQL 9.6.1

PHP version: 7.1.0

Nextcloud version: 12.0.0

Updated from an older Nextcloud/ownCloud or fresh install: 10.0.2

Where did you install Nextcloud from: Web Installer

Signing status:

No errors have been found.

Are you using external storage, if yes which one: No

Are you using encryption: No

Are you using an external user-backend, if yes which one: No

Client configuration

Browser: Firefox 53.0.3

Operating system: OS X 10.11.6