I have setup a two team game each with several numbers (playing as Snathi Revenge).   I was looking to win via Diplomacy and had already secured 4 members of the other team as allies while still helping my team members with tech and credits.   I had setup a team game as the Snathi Revenge are difficult to play as a major race, having other races as team mates gives that civ. a chance to catch up to the others.  In this game my faction avoided any conflict except with pirates and a returning Dread Lords.

When some of my team members would surrender, they would give me their planets and ships, to the point that I eventually had the most powerful fleet in the game.

One of my allies surrender (I still had one ally left from the original team), and all of the sudden my "civilization collapse" ?  That doesn't make any sense since at that point my CIV is the most powerful civ in the game and I have 4 new allies from the other team.  This end game scenario does not make sense definitely not with my faction being on top in military, research and influence and with the second most powerful faction being my ally.

On the setup, I had hand picked my team members, with all of the other team members being selected randomly.