There are plenty of reasons, why a game was not rated. Here is the official list in technical order:
- game had too many desyncs
- game had wrong victory condition (e.g. sandbox)
- fog of war was disabled
- cheats were enabled
- prebuild was enabled
- norush was enabled
- unit restrictions were active
- map was unrated
- game was too short
- mod was unrated
- game was coop
- game ended with mutual draw
- single player game
- game mode was free for all
- teams were uneven
- unknown results (as in "there was an issue with the server receiving all game results)
- teams were unlocked
- game had more than 2 teams
- game had AI players
- civilians were revealed
- wrong difficulty (hu, I have no clue what that is)
- expansion was disabled (same here)
- spawn positition wasn't fixed
- other
In particular the reason "unknown results" is an ongoing issue with FAF as we seem to have problems to get game results sent to and parsed by the lobby server