On occasion, using rcon cli or rcon libraries for python, and even python-valve the rcon server returns empty byte responses and causes exceptions with these libraries.
It's hard to pin down when it happens, rcon-cli has been the most stable but still on occasion gets a dead response from the PZ server. It will return nothing, then you can run it again and it will complete. Not sure if its a resource or timing issue.
Steam Latest, dedicated server on ubuntu
Version: 41.61
Using steamcmd