Ok, looks like it's fixed.
There was a loose diode on the wall target - just a teeny bit loose. I didn't do a good job soldering on the new target switch.
I really have no idea what the problem was though originally. Was it the wall target? Or the lock targets? Or both? I've tested and adjusted all of them. But one of the problems for the last 24 hours has probably been the wall target.
Thanks for the help everybody.