I have run into this bug several times. Sometimes the Spider-tron will not spawn for either level. The second time, either one or both do not spawn. This prevents me from finishing the level. The cure I have found is restarting the game, for me this has always fixed the problem.

Thanks! What was your framerate like when this happened? I think I have seen it happen once.

I do not recall any frame rate drop when going up the elevator(presumable when they spawn). This may relate to an issue that some of the spiders are upside when I enter the area. This may do with how they walk when they spawn because I did see one flip itself over during a battle(it was not at all damaged)