AD synchronisation not running

[bista]

Hello,

I have some issues with my servers synchronisation. I have two Zentyal 4.0 servers, one additionnal and one secondary server. The problem i'm facing is the active directory synchronisation. The secondary server doesn't synchronise anymore with the principal, unless i forced it by restarting Zentyal service or enabling kerberos tickets. I've not been able to get through it.
Got confuse and need help.

Thanks