I was using UT2 and receiving the same loss of traffic in EFB as reported by other users, when flying the 737NGX.
Just recently I uninstalled UT2 and went back to MTX5.3b. AI traffic is now displaying correctly in EFB throughout the entire flight. I have conducted about six flights using MTX3b and EFB has performed flawlessly.
One further note: I tested the 737NGX, UT2 and EFB in the Prepar3d program and again EFB displayed the AI correctly throughout the entire flight.