DAVdroid 1.3.6 now ignores invalid PREF values. Please update to the latest DAVdroid version and synchronize again.
Can Cal/CardDAV be used with ownCloud 10 as on your tested services, it only covers 9 and below. I cannot get it to work with ownCloud 10. The error I am getting with DAVx5 is “Couldn’t find CardDAV and CalDAV services” when using ownCloud 9’s configurations on ownCloud 10.
I can’t imagine why it shouldn’t work with Ownclou 10. However, without logs and more details, I can’t say anything reliable about it.