So the problem with my map is you can choose between team blue and team red, but in 1 round when you run into the team selector to join this team, nothing happens, you are not assigned to a team, but from the 2nd round it works somehow again.
It seems that your Spawn pads are loading before your Team Selector devices. To solve that, you should try by changing the Priority Group for both you Spawn Pads and Team Selectors so the Team Selectors have a lower number than your Spawn Pads (a lower number means higher priority).
Another solution could be to remove the Spawn Pads and Team Selectors and adding the Team Selectors before the Spawn Pads. This is because the game loads first the devices that were placed in your island first.
Let me know if that solves the issue or if you need more help!!