I have been playing and troubleshooting this game for a decent amount of time and would love to help if I can. I have had many friends recently also have a similar issue that we were able to resolve with a few steps (if it is indeed the same issue I think you are describing).
I would recommend the following.
1- Close game and verify its file integrity on steam.
2- Open the game and play awhile and spawn units on single player academy map.
3- Restart the game and attempt your Brooklyn or Manhattan.
This has helped/worked for many of my friends.
Is this your issue or can you not start the game at all?
Thanks. You help me Micheal W. regards from Poland
This did not help me any other options