Thanks Damian,
I’m using Optisystem 13
I’m not sure if you enabled noise in optical Amplifier or not because i disabled it.
The multimode fiber is working as Few Mode Fiber and supports only 6 modes (LP01,LP02,LP11a,LP11b,LP21a,LP21b) which can work for long distance.
Please enable EDFA Noise and check the MMF noise bins error.
Best Regards,