• Duplicate vmkernels MAC addresses found in the same vCenter on different ESXi hosts.
• Currently there is no MAC collision detection in vCenter for vmk interfaces and there is no MACpool for vmk interface. So there will be MAC collision if  the  environment's scale is large.
• ESXi host can only make sure the uniqueness in one single host if the MAC is generated by the ESXi host since the host doesn't hold the information about the other hosts within the vCenter.

This is caused due to no mechanism in place to validate the uniqueness of the vmkernel MAC address across the vCenter.

This is a known issue.
Currently, there is no solution.

To workaround this issue, change the duplicate MAC from the affected vmkernel(s).

Dropped packets, Impact on the storage, VMs ..etc.