Several users have confirmed P3D works just fine for them now.
There are still issues I don't fully understand with P3D4, an extremely long time to regenerate the model cache, which is P3D4 should be even faster than P3D5, and that might cause a crash on start, but we are looking into that.
I must say we always used P3D V5 during testing with P3D+MSFS together, so it's to be expected things to be a bit rough on V4.