Can not sign-in from IPhone 6 to Lync after goDaddy certificate renewal

Having an issue only with IPhones. Android and Windows full client works ok. goDaddy renewal process change our root from old one to G2.

IPhone logs contans:

2015-06-10 14:09:27.341 Lync[584:35b6d9dc] ERROR APPLICATION CUcwaAutoDiscoveryGetUserUrlOperation.cpp/325:Request failed.  Error - E_SslError (E2-2-2)

and

2015-06-10 14:09:27.376 Lync[584:35b6d9dc] INFO UI CMUIUtil.mm/387:Mapping error code = 0x22020002, context = , type = 201
2015-06-10 14:09:27.377 Lync[584:35b6d9dc] INFO UI CMUIUtil.mm/1691:Mapped error message is 'Désolé... Nous ne parvenons pas vérifier le certificat du serveur. Contactez votre équipe de support technique.

or in English

We can’t verify the certificate from the server. Please contact your support team.


The issue was solved by installing goDaddy G2 CA intermediate certificate alongside with new certificate in Reverse Proxy and reboot.

Refer:  https://support.microsoft.com/en-us/kb/2965499