While this could be due to a plumbing issue another possible cause for the strange numbers could be an impending turbo failure.

Since different turbine and compressor pressures create different thrust and shaft loads on your turbo bearings there is the chance that a bearing failure could also be causing your strange numbers.

It would help you to figure out what is up if you temporarily move your boost guage to the compressor outlet and/or where the wastegate is attached so we can get a better idea if this is related to the pressure the turbo is putting out or something that is happening on the way to the manifold.

 

I found that a faulty boost gauge was the cause of my engine blowing up.

The gauge said 15 psi, but had to be way higher than that being I melted a piston, but yet run enough fuel for 20 psi at least...