Because DAVdroid changes all kind of stuff in every new release and radicale too, they did not worked anymore together, when I tried to use DAVdroid 0.6.4 + radicale 0.9.1... Why? Because DAVdroid does now this .well-known path discovery, which is totaly fucked up imo but okay... radicale creates some folders but fucks up everything too and boom you got a problem.

But thats not all. Somehow the ACL Management is fucked up too if you use this .well-known stuff... Anyways. To fix the Problem some things where needed:

• radicale from git (I'm using c932ba230e7780f233c25b9e3e4cb20a62e6a27e now)
• Set ACL type to None or authenticated

In DAVdroid use https://<your-server-dns>/<username>/ (with trailing slash) as URL.

It seems if DAVdroid accepted your config one time, it works for ever... I was just in the need to reinstall my phone, so i installed the newest version (which i had before on my old ROM as well). But the difference was, that i set up DAVdroid with Version ~0.5 and just updated it. It seems the only great problem is in this auto discovery stuff (y u no have custom config dialog then?!)...