I solved the problem: some owncloud app added an invalid character in the xml answer to the client request. now it works great, thanks for your efforts!
I used a Baïkal CalDAV Server together with the Thunderbird Calendar for years. To synchronize my mobile phone I use DAVx.
Suddenly the Thunderbird Calendar did not work anymore while the Etar
Calendar synced with DAVx was still working.
I took quite a lot of time to find the problem. The Calender Server used a port number of 10080. When I tried to access the server from Chrome or Firefox I got “ERR_UNSAVE_PORT”. It seems that Thunderbird Calender also blocked
this port. So changed the port on the server and all is working again, but
DAVx does not update my mobile calendar anymore.
I did not find a possibility to update the port of the BASE URL in DAVx.
Is there a config file, where I can change this with an editor? I have a Terminal app and BusyBox running on my lineage version of my mobile phone.