I was facing a similar issue just yesterday when I tried to access the nodemap of the device using device.stream().ring_buffer.
The fix for me was to store the device.stream() in a seperate variable.
The reason is that in python you can not be sure about the lifetime of the stream object.
As soon as you store the stream in a variable this problem should be gone.
This might also apply to the open method… maybe device is already disposed or one of the arguments you use for the open method, not sure on this one.