@dnutan: that worked for me. Had the same problem on one of my servers… disabling the deltarpm for nethserver-cockpit installed the new version and after that all other updates could be installed too.
Worked for me too. Thanks for the tip.
Matthieu G. (en mode mobile)
Removed cockpit.
Unlocked release update.
Updated server.
Reinstalled cockpit.
No errors or updates to do.
Thank you guys, the problem should be definitely fixed on next cockpit release.