FIFO does not seem to work

I'm using MPU-6000 with "C" as a revision printed on its lower right corner.
User guide says "Use mldl_cfg_init_umpl_6050a2.c with MPU6050 revision A, or any MPU6050 with 6-axis fusion."
It also says: "Use mldl_cfg_init_umpl_6050.c with the MPU6050 revision B. The MPU6050 revision B is required for 9-axis fusion."

I want to use 6-axis fusion (gyro and accel on MPU-6000 and no external sensors). Should I use mldl_cfg_init_umpl_6050a2.c or mldl_cfg_init_umpl_6050.c?

Is there anything I should #define/#undef to make it work?
I get gyro row data through inv_get_gyro_sensor() but only zeros when I use inv_get_gyro or inv_get_accel. I was receiving zeros only through inv_get_gyro_sensors too, until I commented fifo_obj.cache |= FIFO_CACHE_GYRO;

I wrote twim functions for my platform and verified that they work for any length (multibyte operations) in range. I do not use non volatile memory so my ustore functions do nothing (reading returns 0, writing does nothing at all)

I believe I did everything according to User guides/specs avalaible at the beginning and since it did not work I started experimenting. Are there any options I should enable/disable in my situation to make it work?

Has anybody used MotionFusion library as is, implemented platform dependent twim functions, and timing functions and it happen to work right away?