Ok, this problem is now fixed and DAVdroid shows a 404 error notification when a multi-get response indicates status 404 for a requested resource.
However, then there’s the question: Why does DAVdroid request /SOGo/dav/maxmuster/Calendar/personal/11? The preceding PROPFIND response doesn’t even contain /SOGo/dav/maxmuster/Calendar/personal/11.
If you look at your server’s response on the file-listing PROPFIND, you can find:<D:href>/SOGo/dav/maxmuster/Calendar/personal/http:/tracks.example.com/tracks/todos/11</D:href>
This seems to be a server error. Calendar/personal should contain the resources directly, and not in a directory structure called /http:/tracks.example.com/tracks/todos/. Apparently, there’s something wrong with the TODOs. If http:/tracks.example.com/tracks/todos/11 is the file name, it should have been encoded.
DAVdroid expects the requested files to be directly in the requested folder (since it sets Depth: 1), so it requests <folder> + /11 (where 11 is the file name). This requests fails with 404.
Summary:There was a DAVdroid error in parsing the multi-status response. This has been fixed in fb33767e571b91cb78e267a05505e10c91ad3e16. There’s still a problem on the server side (with TODOs, details see above).
Do you agree? Can you please open an issue in the SOGo bug tracker, providing the DAVdroid logs and this issue as reference?