Ok, First, if the OSS is set to null, ensure you exit steam. Also, if this is using the menus, this doesn’t seem to work right inside the editor so you need to use command-line to work correctly.
Ensure you have deleted binaries and Intermediate folders.
Check your code against the end of lecture as well to see if you’ve missed anything.
Re-watch some of the videos (probably last couple) to see if there was anything around blueprints.
Ensure the server name you are adding via blueprint is identical (case matches, no extra spaces and so on)
Give all this a try and let me know how you get on. Also, keep an eye on this thread as we are investigating: Connecting Works, Can't Go To Level
It doesn’t seem to affect everyone as I was able to create a 5.3.2 project but others cannot get it to work.