I figured out that on ubuntu 16.04 + gnome-shell, on the start up there is /usr/bin/gnome-keyring-daemon –start –components=ssh.

I figure out that removing –start –components=ssh was allowing to save the password, visible in the seahorse app

Source: ownCloud Sync client 1.5.3 for Linux won’t remember password · Issue #1590 · owncloud/client · GitHub