Problem solved. It was the OpenTasks app.
SOLUTION: In the permissions settings of the OpenTasks app the option “Contacts” (in german “Kontakte”) has to be turned on.
Thanks for your help.
I use DAVdroid 1.6.4-ose on a Huawei P9 Lite with EMUI 4.1.1, Android 6.0.
I read how to debug but it looks like it doesn’t work. I activated log to external file but if I choose show debug info it shows old informations from July 2017.
How does the debugging work with DAdroid?
I deleted (moved) /sdcard/Android/data/at.bitfire.davdroid/files but show debug info shows furthermore the old informations from July 2017.
In at.bitfire.davdroid/files a new file is created which only listed versions and current versions of the DAV-accounts. The file isn’t updated for 2 days even though I did some manual syncs since.
What I’m doing wrong?