Tested in companion, could not replicate the problem
I see a problem in these 2 events:
Which events should fire when Saucer Sprite reaches an edge?
In what order?
Maybe you need
and move all the saucer logic to the other event?
Also, if I remember Space Invaders properly, the Saucer's edge reaction at the sides of the board differ from the saucer's edge reaction at the bottom of the board. You are missing edge value tests in your logic.