sounds like the VLAN for VXLAN isn't trunked for traffic, or for multicast isn't allowed across hosts. MTU would cause fragmentation, and sometimes failure.
there is a feature in vCNS to test the virtual wire. you need a VM on the wire on all hosts in the cluster, then you can test single host ping and multicast ping ... using VXLAN minimum and standard packets.
I'm trying to find a blog or something that shows where this is so you can test the vWire without using the VMs and actually test that VXLAN is working.