@felmue
yeah, you are right. On the M5Stack Grey there is no wiring between the pins. Could you provide some images of the board where one can see how you did the soldering? time to rip my m5stack grey open and do some soldering too :)
For the next version of the M5Stack there has definitelyto be a wiring between the IMU (mpu9250) and a pin like 35!!