You could temporarily install a mechanical gauge to verify oil pressure reading unless you already have one.

If it's not a problem with your sensor or wiring it could be a collapsing oil line on the suction side. If the line is collapsing some have inserted a coil spring inside of hose or Peagasus Racing has teflon oil hose all sizes are rated to 30 in-Hg vacuum service up to 130°C (266°F). Temperature range -45°C to 170°C (-49°F to 338°F).

I have new lines to do the five year rubber soon.  I thought it odd that it did not seem to drain down to the crankcase in two days time which might fit with the collapsed suction line theory.  I neglected to add that it has an oil temp thermostat.  Strange part is that the pressure was fine before a simple routine oil and filter change.

Check out this from 2 weeks ago.

912 100 HP Low oil Pressure under power

I replaced all the oil lines and the problem is now gone.  Thanks so much for your advise 

Stay safe /Fly often 

Let us know what you find out.

Since the one thing that changed (besides the actual oil) is the filter, you might want to try a different filter before changing all the lines, etc.  It's possible that there is some sort of defect in the new one that's restricting oil flow at times of high demand.

With another new Rotax filter and topped off oil level I had normal pressure on start up and after warm up.  Static run up between 4500 and 5000 produced pressure just above minimum with a 20 psi drop from idle speed pressure.  Psi returned to normal with rpm decrease toward idle speed..