Sounds like some kind of switch matrix issue. The start button and lower eject are in the same row. Do any of the other switches in that row cause the eject hole to fire?

When you press start in switch test, what switch numbers register?

It's the switch in front of the kicker under the upper playfield on the left

Were you able to get into switch test? If not I could try to make a video of mine showing it

Now that you've got those cleared out, try hitting the start button, lower eject, and hidden tomb switches, see if each one only registers the correct switch