I and others have the same issues,
The first time I press start game all is fine, then when I end game and start game again all players switch to spectate, then I end game and start again and all is fine, then again and it spectes
To put simply, on the 2nd, 4th, 6th etc time I press start game all players always switch to spectate but on the 1st, 3rd, 5th round all is fine