when I add a device using the logicmonitor Python SDK, I see the property values have been successfully added when I manage the device on LM
I created a test script to just 'println' the properties and it gave me the correct values.
I personally have not used the Python SDK (I'm more a PowerShell person). But based on that you see the properties in the portal for the new device and your test script is working, I would assume your script above is fine at this stage.
Do you have more details on what you mean by "the scripts that need the properties to run do not seem to work"? Are these more Python SDK scripts or perhaps custom DataSource scripts that attempt to look for those properties? What does that code look like?