Hi,
I am having exactly the same issue. P3Dv3 3.4.18.19475, FSUIPC 4.959. Reinstalling FSUIPC is the only thing that works for one time only.
However, I noticed, that trouble started when I installed some more scenery via Orbx FTX Central v3 (FTX Pacific Northwest and Pacific Fjords to be precise). I also use chase plane and every time after I installed some scenery and start P3D, I get a notification from chase plane that WideViewAspect=true was missing from my prepar3d.cfg. However, I didn't made any changes to that file. I highly suspect FTX Central v3 3.0.2.2 being the cause of my trouble. I also noticed that after the FSUIPC installation, my Prepar3D.exe is not set to start in admin mode anymore (which never happened before using FTXCv3). Do you guys use Orbx?
Regards,
Jan