I did find the cause of the issue but have another question.
Tonight I went to the hangar and checked to see if the electric pump would show fuel pressure and sure enough it did which makes it hard to find the problem.
Dynon confirmed that if the electrical connection was not working it would show a red X on the screen.
So I started checking flow in the lines to see if there was anything plugging a line.
I started at the manifold bolt on the top where the fuel flows to the sensor and the return line back to the tank. It looked fine.
Next I pulled off the fitting at the fuel pressure sensor and an orange-ish colored gel came out.
I removed the fuel pressure sensor completely and cleaned it out. Here is a picture I took with my iPhone that shows some of this gel like substance in the pressure sensor.
Now the events from last Tuesday make more sense. It was an early morning flight. The plane had been sitting in the cold hangar which most likely caused this gel to harden to the point where the electric fuel pump would not allow the sensor to see the pressure. Once the plane started, the additional pressure from the mechanical fuel pump pushed the gel to the sensor. Then after shutting down the gel had been moved or dissolved enough to see the pressure from the electric pump only.
It has been warmer (in the 50's) the past few days which is most likely why we could not replicate it.
Now the question is where did this gel come from and will it come back?
We are burning auto gas with ethanol in it. Has anyone seen this or have an idea where it comes from?
I plan on checking every 10 - 20 hours to see if it returns.