Inconsistency between I2C (imu) and SerialUSB.read()

I'm not sure what your problem is. I'm not sure what a NUC is. Please try again to explain what you want it to do and what it actually does. If you have different configurations or you are commenting out different lines, please say what you expected that to do and what it actually does.

The problem is certainly somewhere in the code you didn't post.