Weird Gyro Issue

Hi all, we are having some problem with one of the fmu-v2 pixhawks. During our flight tests, this octorotor can do whatever we want to test. However, some occasions it refused to arm and show some generic EKF2 error. Although the octorotor is on the ground, from QGC we can see the attitude is doing “roll” continuously. We tried to reboot several times and eventually this disappered.

In the effort of figuring this out, we did an indoor test: just power on the drone and leave it there to monitor its status. After several tries, we were able to reproduce the same issue and managed to take donw the log. From the log, we can see that the Gyroscope-X started to have a huge bias after some time with no reasons.

log can be found here:

Is this a hardware problem? If it is, why is the behaviour so inconsistent?

Really appreciate any help or advice. Thanks!