Do Multiple-Whonix-Gateways Require Different Whonix-External Virtual NIC's?

When setting up Multiple-Whonix-Gateways following the whonix docs (KVM) it recommends only changing the internal network to route packets from Workstation to the correct Gateway. Is there no problems with having two Gateways using the same NAT Virtual adapter to send traffic?

It might be something else but when I run more than one Gateway at the same time one seems to block the other’s traffic.

Any advice on how to test if this is happening would be appreciated.