Invader Issues

I'm using the invader movement in a game and have run into what I have to assume is a bug.
Everything was working fine until I added some other invaders. At first they were all working fine together, then (somewhat randomly) the movement behavior for all of them changed. No matter what I set their start direction to they immediately move left until they hit the side of the frame, then move down rapidly.
I tried working through several possible solutions, like applying a movement controller object, adjusting all the invaders' movement settings and even deleting all the new objects and events. Nothing seems to have any effect. I even tried changing all their movements, then changing them back, hoping to "reset" the movement somehow.

If anyone has any advice, it would be super appreciated. I'm trying to get this done in time for the Ludum jam this afternoon.