VMWare COM port forwarding issue - vsphere 6.0 and windows 7 guest.

VMWare COM port forwarding.  

We have a customer with an Opera IFC server which was on a failed vSphere 5.5 host.  I've rebuilt the host and lit all the VMs back up on it.  However, their opera interface can no longer communicate with the vm.  I then realized that 1 of the 9 IFC connections (the one that isn't working) is RS232 serial, so I added the uart0 from the host to the VM.  I rebooted the VM and COM1 and COM2 ports show up.  I thought all that was over with, but now the customer is telling us that the Aloha system hasn't worked since the rebuild.  I rebuilt the VM host using vsphere 6.0.

To test, we plugged a known working loopback adpater for the serial port and tried establishing a connection.  The port immediately closes the session and says the COM port is not ready.  

I'm using UART0 on the vsphere host and I'm using COM1 on the IFC vm.  I've not changed any of the settings on the VM from adding the COM port.  This should just work, right?  

FYI- I'm currently awaiting a window in which I can reboot the vm.  Unfortunately, there are 8 other interfaces which must remain up as this is hospitality.  

Thanks in advance!

Chris