Can't contact LDAP server

Hi,

I'm managing 30 branches, all connected via MPLS and running FGTs as firewalls.

There's a main site with a DC (10.7.7.80).

I wanted to authenticate fortigate administrators via LDAPS and use their AD accounts for login.

However, it is working in some of the sites, and not working on the rest.

If i check the logs on the main site, I can see the packet is accepted

but I can also see this session timeout if I click on this line of log:

Some of the FGTs are able to contact the DC, when I look on their logs, it looks the same just without this "session timeout".

I tried to increase the ldap query timeout on appliances which have this problem:

 set remoteauthtimeout 15

 set ldapconntimeout 8000

but still the same.

Will appreciate any help and advices.

Thanks!