I made more flights last evening in Normandy using different aircraft among those available during the free month, and although I had performance drops a few times, it did not last beyond a few seconds during the flight. It was not critical and persistent like the other day.
My quick missions had only ground vehicles and it was set to Max and I was alone, no wingman...
So no idea if it's aircraft-related
or:
Also, I noticed when I use the canons at low altitudes the performance sometimes, but I was flying fast toward a passing by train. So the ground vehicle could be the cause...
Another possibility, some air bases or specific locations might be causing this perhaps. It could be the presence of vehicles or another factor.
The altitude transition could be also a hint who knows...
Could it be the online connection to servers although I was flying solo.
But all these are simple speculations because this performance drop during some flights in Normandy does not seem to be consistent or based on a pattern that I could identify.
Also, I got many crashes to desktop with a bug report dialog only when I was generating a quick mission in Normandy. Also, I could not find a pattern for this.