Slight possibility of air pocket in pressure switch that you lost when you shut it down then re-started it?
I'd plumb in a mechanical gauge temporarily. I bought one from Jeg's, Auto Meter I think about $40. Uses skinny plastic hose with 1/8" pipe thread fittings.
I also bought an AN-8 adapter fitting, male on one end, female on the other with an 1/8" female pipe thread in the middle.
I can test my oil pressure in any spot of my system now.