New iPhone does not sync with personal WebDAV server


i changed my iPhone to a 6s plus and i am unable to sync on my personal WebDAV server (iOS version 9.3.5).

Ominfocus 2.15.2 for iOS tries to sync for a long time and ends by telling that the request has expired.

I checked my prefs which seemed ok (the same as the one on Omnifocus 2.6.2 for mac which syncs perfectly). I re-sent the settings from my mac by email but sync was not working.

Any idea ?