Of course it's going to happen again.I too think there is a problem when minimising the window. On one flight, I barely minimised the window and landed with about 30 FPS. I left the P3D window minimised for about 30 mins and when I re-opened the window the FPS had dropped to 20.
I'll have to see if it is reproduce-able, because at the moment I don't know if it is. But my findings seem very similar to what Keller5678 has found. I shall do some more testing.
But at least my P3D doesn't crash any more. I was plagued with P3D crashes since version 3.4. Version 3.4 has been the WORST version released in P3D's history, it is absolutely plagued with bugs and unfortunately it is damaging LM's reputation especially for the up-coming version 4.
The solutions are simple:
1) LM should make sure that P3D works same in all "states" (in all honesty, this shouldn't be a priority!!)
2) don't minimize
I do 2nd. Never had a problem.