unexpected_ball_on_playfield event is causing ball count to be greater than balls_installed in the game preventing a game from being started.

[mythmaker9]

If a ball device on the playfield registers a switch hit unexpected due to a temporary or unknown hardware issue, MPF is throwing this event:
EventManager : Event: ======'unexpected_ball_on_playfield'====== Args={}

This is causing MPF to report a ball on the playfield and ultimate increase the ball count in the game.

This occurs even if a hardcoded value is set in the machine configuration such as:
machine:
balls_installed: 3
min_balls: 3

This will prevent any games from being started ever on the game even if this switch hit only happened once temporarily or is an intermittent issue (think light hitting an opto, etc).

[jabdoa2]

Capping balls at balls_installed might work. Maybe even a max_balls parameter? But that would require additional warnings/error states when we actually find more balls than expected.

This will prevent any games from being started ever on the game even if this switch hit only happened once temporarily or is an intermittent issue (think light hitting an opto, etc).

That is only partially true. If you enable ball search it will resolve this condition (disabled by default to prevent it from hurting builders).