I was getting OOM's which seemed to be caused by Plan-G. I have now flown for six hours with only P3D2, Plan-G v3.07.71 and Opus v3.36.1 running without a problem. I have set Plan-G to File --> Options --> Map Provider --> OpenCycleMap and the OOM's which I thought might have been Plan-G related have vanished. Of course it might be a coincidence but it is worth a try.

Are you able to read in P3D v2 flight plan files (.pln) with Plan-G? It does not work for me.