Oh, but it was indeed a glitch by Google Contacts !
I’ve uninstalled the app and reinstalled it, and now all works well :-))
Thanks for making me check and for your quick reply.
I installed davdroid on my phone to sync my calendars using caldav. Server side I got a horde server.
My old phone use caldav-sync and it work well.
On the new one I install caldav sync without result so I tried davdroid and the calendars are only sync from the phone to the server (which eliminate any permissions problems).
I have no clue what to search for in the logs.
Any direction would be appreciated.
I use the last version of horde on Debian Jessie (updated yesterday)
I use the last version of davdroid available on the play store.
My phone is a nexus 5x using android 7.0
Here are the debug information from the app (expiring on December 22th 2016) :
Prolem solved. No more need for debug info.
Okay solved the problem myself. It may be useful for someone else.
I am a bit paranoid so my server have a strict firewall blocking anything that has not been white listed. Even on output.
Horde need to synchronize the timezone using caldav. There for it tries to get timezone infos using a ftp:
It was blocked by my firewall and therefore blocking sync.
thanks for the app