Syncing account on dav.openxchange.eu

Hello, did anyone ever sync an account on openxchange.eu successfully? I ran into the following issue:

error: The server returned something vdirsyncer doesn't understand. Error message: InvalidXMLResponse('Invalid XML encountered: mismatched tag: line 1, column 2777\nDouble-check the URLs in your config.',)
error: While this is most likely a serverside problem, the vdirsyncer devs are generally interested in such bugs. Please report it in the issue tracker at https://github.com/pimutils/vdirsyncer/issues
error: 1 out of 1 tasks failed.

I have similar problems with other Cal/CardDAV clients as well. Each of these not managing to find the avilable address books and/or calendars. The only working client I found is OX Sync 1 that offers a distinct selection of providers. This selection includes EuroDNS which is behind openxchange.eu.

OX Sync uses dmfs 2 which manages to connect to https://dav.openxchange.eu successfully. So I started to reverse engineer it a bit, trying to find out which URLs it attempts to connect. Unfortunately, I could not find out.

Before spending more time on this (taking into account my lack of knowledge about Cal/CardDAV): Has anyone ever synced an account on dav.openxchange.eu successfully?

Start by reproducing the failure against https://dav.openxchange.eu and inspect the malformed XML response, comparing the discovered endpoints with the working OX Sync behavior described in the issue. Done means identifying whether vdirsyncer can support this server or documenting the server-side incompatibility and the relevant configuration or endpoint details.