Same here 
After updating two Nextcloud instances, both have problems with Thunderbird Sync
(Lightning - Calendar 5.4.1.1 “CALDAV” & SOGo Connector 31.0.4 “CARDDAV”).
Calendars are no longer displayed (disabled) and reactivate fails without error!
After creating a new app-pin in Nextcloud and deleting the saved password in Thunderbird, you will not be prompted for a new one?! It seems as no connection could be established.
Little note on the edge if it’s related 
When I call the calendar URL in Firefox, I get the following text:
This is the WebDAV interface. It can only be accessed by WebDAV clients such as the Nextcloud desktop sync client. CLEAR!
When I call the calendar URL in IE, I get the following text:
Unauthorized ?
There are no entries in the Bruteforce block list!
Maybe Thunderbird requests also receive this message?!
The sync on the mobile phone (Windows Mobile 10) works without problems!
@nickvergessen
Unfortunately, the comment out solution did not work for me, same problem 
Does anyone else have an idea?
I suspect the constellation Thunderbird Lightning & SOGo should be quite common.