For others who may be struggling with various weird issues, when they say don’t mix GameMode and GameModeBase classes in your project, please listen to them 
I only realized I did this by mistake after changing some play settings and un-checking ‘Run Under One Process’ which gave me a handy console log that had some error in red text.
Turns out when I made a new blueprint for a game mode, I accidently used ‘GameMode’ instead of the ‘GameModeBase’ which I normally use.
The errors I were encountering were:
-Clients main menu widget would not show up.
-All print statements would be labeled ‘Server’ on the client side.
-Client main menu widget finally showed after the server side changed maps.
So take this information and use it, I was stuck for a day on this one…