@shanegranger Thanks for confirmation. I think this must be something strange going on between YAT,Windows and the comm port. Testing using YAT on my (Windows 10) machine, if the Duet is just restarted it sits on "receiving" after a M115 command is sent for just under a second then prints the output. It looks like YAT is receiving the response form the Duet but not seeing the end of the communication.
Looks like you have got this sorted anyway by using another terminal program.