Well, I have just switched to DAVdroid it I like it very much. I have switched from CalDAV-/CardDAV-Sync.
I am using the latest DAVdroid version 18.104.22.168 from Google Play. Installation was very easy and straighforward compared to the above previous sync tool and everything runs fine except one thing: I am not able to sync calender entries elder than 90 days. Whenever I increase the limit to e.g. 120 days I am getting permanent sync errors that I cannot interpret. As soon as I reduce the limit to the default of 90 days everything runs fine again. I am using DAVdroid on CM 13.0 nightly from 2016-09-24 and my CalDAV/CardDAV server is ownCloud 9.1.3. Sorry for not giving immediately the exact error message, but its late and I just want to know, if it's an known issue. If not, please let me know and I will provide more detailed information.