Proxmox requires subtracting 50 from the MTU so it can store it’s vxlan information in the packet.

From the docs:

Because VXLAN encapsulation uses 50 bytes, the MTU needs to be 50 bytes lower than the outgoing physical interface.

It’s super annoying but I couldn’t see another way of having vms be able to talk to each other transparently regardless of which node they are on