IIRC it's a setting in il2setup.exe, under video options. I just forgot which one(s).
Although I've never had it as a momentary effect.
Might have been the "Vertex Array" tickbox, but you'll have to do some checking. Copy down what you have at the start in that screen, so you can always go back. If you are going to check which it is, it's your call how you go about it.
The binary method is a quick way of finding the source. First you change every setting there, so you can see if it fixes that issue. If it does, you know it's the right source of the problem.
Then you change the left half screen of the settings. The issue doesn't come back, it's in the right half. Does the issue come back, you have the correct half.
Change the top half of the screen-side where the issue is. The issue doesn't come back, it's in the bottom quarter. Does the issue come back, you have the correct quarter.
By now you only have 2 or 3 settings to toggle.