My rover does not pitch properly

[king of nowhere]

For a while I had the feeling that when I pitch up, it was less responsive, But now I noticed, it's really like that

In this first image, I am pitching up. You can see in the box in the bottom left corner, the gauge for pitch is barely moving; the rover is applying a lot less torque than it could.

Here instead I am pitching down, and it works normally.

Yaw and roll work normally.

I tried going in space, it still malfunctions.

i tried to launch a new copy of the rover, it works normally.

I verified by spinning around in space, the effect is real. pitching up is noticeably slower than pitching down.

So, there is some kind of bug where my rover is just not applying its full torque on the reaction wheels when turning in one specific direction. And it's a bug that happened at some point in time.

anyone has any idea what it could be, how it could have happened, and if I can fix it somehow (short of getting a new rover)?

thanks