WebDAV connection broken in WebInterface after Server Migration

Nextcloud version: 12.0.3
Operating system and version: Debian Lenny
Apache: 2.4.10
PHP version: 5.6.30

I migrated my nextcloud instance to a new server (files with rsync, mysql with dump).
Now when I login to the Web-interface I directly get the notification connection lost from the files app
In the Admin interface I get the message:
Your web server is not yet set up properly to allow file synchronization because the WebDAV interface seems to be broken.
If I try to display the Log in the Web Interface I also get the “connection to server lost” warning and nothing happens.
If I check in chrome dev tools, the console says
PROPFIND /remote.php/webdav/ net::ERR_EMPTY_RESPONSE

Now when I access the webdav URL with e.g. cadaver, everything seems to work.
If I access the URL with the Web Browser directly (so a GET request) I get
"This is the WebDAV interface. It can only be accessed by WebDAV clients such as the Nextcloud desktop sync client."
I assume It seems to be a problem with the PROPFIND request from the browser - but none of the DAV modules is enabled nor did I find a Limit directive in any of the configuraiton files.

Also connecting with the Windows Desktop client does not work, it says
Failed to connect to Nextcloud at http:///status.php: Connection closed

Unfortunately there are also no related messages nor in the nextcloud log, apache log files or syslog.

Any ideas what could be the issue here?

Sorry I still was not able to find a solution.
In the meanwhile I tried several things and also suspected that the PROPFIND was not allowed.
But this is not the case - with a Rest Client I cann issue the PROPFIND call against the WebDAV URL - still the browser gets an empty response.

May it be that there is some issue with transferring the authentication between calls?
Also the /index.php/apps/systemtags/lastused gives an ERR_EMPTY_RESPONSE in the Browser…

Ok, the issue is resolved now.
It seem that it was an issue with SSL.
On the old server SSL was enabled for the virtual host on the new one not yet - after re-enabling SSL everything works again…
It would have been nice to get a more meaningful message in this case…