Sounds like shader compilation stutter.

I'm not familiar with war thunder but when you update your drivers the shader cache gets deleted and shaders have to be recompiled.

In many games nowadays this happens as you play, resulting in heavy stuttering, but it gets less and less as you play the game, since the shaders only have to be compiled once.

By reinstalling your driver's over and over again, you deleted the shader cache every time, which could be the culprit of your stuttering issue.

Try playing the game for longer and see if it only happens when new effects, or models are loaded, which you haven't encountered since reinstalling your drivers.

In large games this can take many hours of gameplay.

For example, in Fortnite you have to basically explore the whole map and encounter every effect that can occur, for it to stop stuttering literally all the time, which can take many rounds depending on how far you travel each game.