Mahony Algorithm - The rotation angle becomes unstable when rotating the device quickly

I'm new to sensor and IMU, so my question is probably very important to others, but this has puzzled me for a few days now.

I am using Mahony's algorithm to calculate the Euler angle of my device; three corners look correct when a static device is static or slowly moves / rotates the device; however, the pivot angle will be unstable and irregular when the unit is rotated quickly. Can anyone help me solve this problem? My device uses the MPU-9150, I use the 6 parameter method of the Mahony algorithm, that is, only the gyroscope and accelerometer are involved.

This type of question is difficult to solve without debugging real code. So, I'll pay $ 500 for anyone who can meet me and help me find out the problem in my code (IOS); I will also pay for any shipping and other expenses. But please make sure that you have experience in this topic and are confident in solving the problem, otherwise I will only pay a part of the money.

I live in New Jersey, so anyone from New Jersey or New York is welcome; please leave me a message if you would like to help.

thank,

Dihan