Korganizer and open xchange

Hello,

I used Debian Jessie before and Koragnizer and Open-Xchange works great (also with contacts). Since the upgrade to Debian stretch (korganizer 5.2.3) it doesn't work anymore. I got the following error message: https://bugs.kde.org/show_bug.cgi?id=333408, but this bugreport handle only the uncompletet errormessage and not the problem why this is happen. When I try to use normal CalDAVm I got the Error-Message: 

There was a problem with the request.
(405).

but with owncloud it works well. 

I use korganizer/kontact version 5.2.3 and Open-Xchange version 7.8.2
Can somebody help me to fix this problem?

best regards
Stefan