>>51373
Based on that stripe of rubber hoelding the flex, I assume your keyboard is one of those big flex plastic sheet 3 ply kind of keyboards like mine.
Mine (a nice dell) had that same issue for a while, and it took a lot to fix it.
Basically, its dirt or moisture or both. You will have to pull out the sheets, gently rub every inch of it inside out and inside out and inside out with some alcohol (70%+ better) until its fucking immaculate, and blow it dry with a cool fan until it is completely and utterly dry. Only then it will behave.