[Evolution] Problem with ownCloud - Sabre/dav

[Mirko Hessel-von Molo <mirkoh math upb de>]

Dear all, 

new to this list, let me first congratulate all evolution developers and
community on this fine piece of software you're working on. Having been
deeply frustrated with korganizer, I switched to evolution a couple of
years ago and never regretted it since.

However, now I've encountered a problem I wasn't able to solve myself.

I'm running two different installations of evolution on two Ubuntu
systems: System A is (still) Ubuntu 14.04 with evolution 3.10.4 on it, 
System B is Ubuntu 16.04 with evolution 3.18.5 on it. On both systems I 
access addressbooks on an ownCloud server via WebDAV. Apparently the day
before yesterday the owncloud installation was updated, apparantly the
new version is now using the sabre/dav framework which it wasn't before.
However, this I can't tell for sure as I'm not administrating the
owncloud server. 

Yesterday I observed that on system B, loads of entries in the contact
list had vanished. They are simply not there any more: Not shown in the
complete list, not found by search, not autocompleted in email To: field
etc. (Many other entries remained there, though. The ratio of vanished
to remaining is about 1:2.)

To check, I added a new WebDAV addressbook with the same URL. It shows
exactly the same behaviour as the one I already had.
As another check, I accessed the owncloud contact list via the web
frontend: it showed me all the contacts I was missing. I downloaded the
contact list as vcf file to see whether there where any conspicuous
difference between entries that are shown and those that are not: I
couldn't find any. When I imported the vcf file into the "local"
addressbook, all contacts showed up. (That's a workaround, at least; but
of course presented me with a nasty synchronisation problem...)

Today, I checked whether on system A the contacts would also have
disappeared: they have not. Up to now, everything is just normal.

So here's what I can conclude: I have a system running a newer version
of evolution that mysteriously only sees/retrieves part of a contact
list on the owncloud server, while  the older version of evolution has
no problem at all. This behaviour may be related to an update in the
owncloud installation.

Both systems are productive systems for me, and I'd like to have both
systems working properly. Therefore I'm willing to spend some time
investigating the problem. How can I go about to debug this? Are there
logfiles for evolution-data-server somewhere, or for the WebDAV backend?
How could I try to produce a "reproducible version" of this error? (I
can't give anybody access to that particular owncloud server, nor can I
share the actual contact lists for debugging.)

Thanks a lot for any help, 

best regards, Mirko