Hyper-V 2016 cannot connect to 2012 R2

I cannot connect a Hyper-V server to another - from 2016 to 2012 R2

They were replication partners but now fail to speak to each other.

I can connect to other 2012 R2 boxes from the 2016 box

i can connect to the 2012 R2 from other 2012 R2 boxes.

All settings are at default config.

I needed to run 'winrm quickconfig' to get WinRM back to normal - no idea what may have changed this????