I kept having issues with the IR Sensor calibration on the MMU2S after the MK3S+ upgrade. To get the sensor to read 1, the holder/chimney had to be pushed all the way to the right and then some. The reading kept fluctuating between 0 and 1 and I consistently had load failures as it was a 50/50 if the sensor would read 0 or 1 at filament load.
I modified the IR Sensor Holder for the MK3S+ (only MK3S+, the holder is different from regular MK3S) to have more length to the adjustable M3 screw holes on the IR Sensor Holder/Chimney. This should allow you to move it more right if needed on your setup.
The author hasn't provided the model origin yet.