I had same thing when I first got mine. Have you done any other mods to it or bought aftermarket parts?
Have you tried all the filaments in the AMS to make sure it isn’t just the AMS primary feeder? Tends to default to the #1 slot so maybe try a different slot. Calibration may not let you do that. Check the buffer to make sure it isn’t hanging up. Can you see the filament in the PTFE tubing? Darker colors you should be able to see the filament run into the toolhead.
Have you factory reset it? Were you printing prior to do the upgrade? If so probably focus on those items. I looked at the parts kit that comes with that upgrade and it looks like they have you replacing some of that tubing.
You can get a long strand of the filament and push it from the back of the AMS all the way to the toolhead and see if you can feel it hitting something on the way.