Quoted from SunMonkeyAZ:
In my case the magnet isn’t activating at all. In my test I lit lock, held the ball over the magnet and hit the switch. If it was a strength or time issue I would have at least felt a little pull and heard the magnet kick on but nothing happened.
Not sure if this is the case or not, and does it take more than just activation of 78 to trigger the magnet for lock? That is, does 71 and 78 have to be triggered within a certain amount of time to have the magnet activate for lock? Maybe to prevent false positives or if 78 gets stuck closed?
I had an issue with a LOTR once where two switches needed to be activated in quick succession for the event to be triggered (Destroy the Ring); just hitting the "downstream" switch (in the backbox trough) wouldn't do it, even though there was no way to trigger the downstream switch without hitting the upstream switch (center ramp spinner) first. The spinner switch was broken, and there was no way to get Destroy the Ring to start without it.
I know you had said that all the switches worked in test mode, and maybe just double-check that as you travel up a ramp, all switches are registering (looks like it should be 72, 71, and 78 if your are going up the left ramp).