MPU6050 DMP stops producing any estimate after correct operation for few minutes

motion_driver_6.12 running in ARM platform
After initialization, the DMP operates as expected, producing INV_XYZ_GYRO/INV_XYZ_ACCEL/INV_WXYZ_QUAT in the FIFO output.
After ~10 minutes, sensors read value from function dmp_read_fifo becomes constant 0, no more measurement available.
In the meantime, no user code made write operation to PWR_MGMT_1, and this register is changing from value 1(correct operation) to value 16 or 32(no estimate being produced by DMP).
Any hints on how to prevent this unexpected mode switching? I want to keep the DMP running until I send sleep cmd explicitly.
Thanks a lot.