MS_RPC_WKST_REACHABLE ERROR for Microsoft Server

[#1]

Hello,

I have a Member which is syncrhonising AD DNS with a Microsoft Domain Controller and the DC is not synching DNS Data with the MEMBER

My microsoft DC is showing up in ERROR mode since 2 days in the infoblox GUI

If I test Microsft Server then all first 3 tests are green

SYNC ENABLED 

MEMBER ASSIGNED

MEMBER ONLINE

except for 

MS_RPC_WKST_REACHABLE which is saying :the specified I/O operation was not completed before the time-out period expired

Nothing has changed in the environment in the last weeks . What could possibly be the issue ?

[#2]

Did your firewall team make any changes lately? 

https://support.infoblox.com/s/article/3811 or https://support.infoblox.com/s/article/3819

I've reviewed a handful of support cases which also had firewalls as RCAs.