@fhollerweger I only know that Privacy Guard has to be disabled for DAVdroid since I know about Privacy Guard (we even had a FAQ article about that in the beginning).
So I assume that if DAVdroid with enabled Pricacy Guard has worked some time, this was by chance and maybe even a Privacy Guard bug. After all, Privacy Guard’s task is block access to contacts and events and thus DAVdroid.
If you find anything about why its behaviour has suddenly changed, please let us know 🙂