IMU vs GPS Fusion

I am running the latest version of PANDA with the PANDA board and a BNO 08x with F9P RTK. My IMU fix is rock steady compared to to GPS fix when running through the field, but when I turn fusion more towards IMU my tractor gets lazy to the line despite my higher gain settings in Pure Pursuit. I would think IMU should steer better in rough ground is anyone else having these issues? IMU located in tractor behind the seat. Also it seems no matter how much tuning I do I cannot get my tractors to drive under ± 2in error. I have 2 setups been running for 3 years now.

I see there was a Arduino roll fix last month does anyone know what bugs were found to prompt this ?

What roll fix?

I have similar observation. On flat ground at 8-10 km/h it drives under ±3cm of the line. In field it drives good on IMU but sometimes it moves from line ±15cm then continues to steer normally on 90/10 IMU GPS Fusion. On 20/80 it drives strait on flat ground ±3cm, but it seams unstable tractor is jittering on the screen and look ahead is set to 3m, speed gain 1.5, need to test on rough ground and 50/50 Fusion.

looks like an update to the Arduino code ?

my best results have been 20IMU 80GPS

There was an update to the Teensy code to be able to choose the roll axis from AOG but no Arduino update as far as I know.

Till now my tractor best works at 70/30