NLB, ADFS, DNS issues?

Hello Experts,

I have a client that after site migration, users unable to be replicated to O365, password synchronization failed . IT team unable to ping VIP of Windows network load balancer.

As workaround, a DNS record pointing to a single ADFS server instead of VIP of WLB was created in the DNS zone . After creating a DNS record, email and dirsync was reestablished.  If we revert changes to original state [ADFS servers in a nlb using VIP address] email, users and password synchronization stops

Company runs ADFS server  [2008 R2 servers] and Exchange Hybrid, Windows 2008 Forest/domain fuctional level

Any ideas on why we are unable to ping VIP of Windows network load balancer? ADFS servers are in a DMZ network, before migration of site everything was ok, they did not change any IPs or any settings on the network load balancer, and the WIndows NLB is setup for multicast on the 2 nodes of the NLB

if the NLB cluster of ADFS was deployed is down, email, and users/password sync will stop, but if anything changed, why it stopped?

How can we fix this issue? do you believe is a DNS, ADFS, or office 365 issue or Windows network load balancer issue?

Should we upgrade ADFS servers to 2012 R2 to fix the Windows network load balancer issue[ if determined is NLB root cause]
Please, provide instructions step-by-step to fix this issue