Really odd -
Try hooking an ohmmeter to the PU coil - engine off. Apply vacuum slowly to make sure it's not losing continuity.

Also - use a feeler gauge to see how far away the coil is from the reluctor. Then measure it with vacuum applied. Too far away it won't trigger.

You can measure the PU coil output - use an analog meter - needle type, a digital will lie) set it to low voltage AC - crank it - with and without vacuum to see if it's different or goes away - should be about the same test as the ohms test, but measuring actual output.

Test the ground wire the same way - black wire - with and without vacuu.