Single ping response from Windows Server

We recently moved offices, and the only changes I am aware of we have made to the network is to move the servers and desktops onto a new IP range 172.50.0.*/23. However, we are now experiencing intermitten and very odd communication between machines.

We have 2 Active Directory domains, and all the servers on one of the AD domains can be pinged OK, and they can all talk to each other fine.

However, on the second domain, we are experiencing intermittent and strange ping behaviours. What we are seeing is as follows:

• Some servers simply don't respond to pings from other servers, but will respond to pings from other machines on the same subnet.

• Some servers respond intermittently to pings from other servers, whilst at the same time responding reliably to other servers / workstations.

• Some servers respond only once to a ping, and then never respond again such as:

  ping mailfilter.intranet.domain.com
  Pinging mailfilter.intranet.domain.com [172.50.0.240] with 32 bytes of
  data:
  Reply from 172.50.0.240: bytes=32 time<1ms TTL=128
  Request timed out.
  Request timed out.
  Request timed out.

• Sometimes I'm seeing slow response times, such as 800ms, which is certainly not normal considering both servers are connected to the same GB switch.

What we have tried is the following:

• Reconfigure the switches back to Factory defaults

• Replace all switches with different switches

• Add devices onto the network one at a time until the issue returns, and there is no pattern. The servers respond to pings fine for a little while, and then after some time the issue returns

• Moving servers from one domain to another, does not appear to resolve the issue for now, although it's only been a few hours…

I really don't know where to turn next. Is it possible there are some legacy IP based rules hidden somewhere which could be causing this?