Cannot connect to packaged binary if using UE4Binary start command: Branch 4.25

[jojoreeves]

• Operating System: Windows Server 2019
• UE4 Version: 4.25.3
• UnrealCV Version: Branch 4.25 dedd72b
• Client (python2, 3 or matlab): Atom/Hydrogen + Python 3.7.8
• Problem Description: Unable to connect to binary after launching it with:
  if os.path.isfile(binary_path):
binary = UE4Binary(binary_path)
binary.start()

client.connect()
returns:

ERROR:init:63:Error: receive a malformat message, the message should start from a four bytes uint32 magic number
ERROR:init:205:Can not connect to ('localhost', 9000)
ERROR:init:206:Error 'NoneType' object has no attribute 'startswith'

I have double checked and the port is in use by the binary. Running Get-Process -Id (Get-NetTCPConnection -LocalPort 9000).OwningProcess in PowerShell says that it is in use by my packaged binary.

If I launch the binary manually and bypass the UE4Binary start commands it connects ok though. Should I not be starting it this way? I pulled this from one of the examples.

[jojoreeves]

It may not be UnrealCV actually. I tried with os as well and I get the same issue:
import os
os.startfile(binary_path)

I was able to work around this with:
import subprocess
subprocess.Popen([binary_path])

The client connects ok now. Not sure why that is though...