RDP won't connect to IP or DNS name unless .local is added but ping resolves the name

I'm having an unusual issue and I'm not able to pinpoint where it is coming from.

We have a network with Hyper-V servers and VLAN tagged NIC cards on the servers and routing between them.

I am able to RDP directly to our second DC but not to our PDC.

If I ping DC1, I get a response.
If I ping DC1.domain, I get a response.
If I tracert DC1.domain, it follows the relevant route.
If I nslookup DC1.domain, it pulls the correct IP from the DC1 itself and DC2 if I specify it.

If I try RDP to DC1, connection times out.
If I try RDP to DC1.domain, connection times out.
If I try RDP to DC1.local, it connects fine.

Anyone know where to start my search for how to resolve this issue?