I’ve gotten this warning a couple of times when there were not broken filament in anywhere. To fix it, I had to manually insert filament into extruder via a y splitter and pull it out again to make AMS happy.
This warning came up again today when AMS retracted filament successfully after a print job. I was simply trying to print another job from the same AMS slot when this warning popped up again.
It seems to be a firmware bug or the filament detector is confused.
I have not had this problem but I have seen others. I was trying to find the post link for you about the metal lever sticking on the plastic housing.
Then I found a video lol 
Thank you! I’ll submit a ticket for a replacement if that turns out to be culprit, most likely it is.
More than likely You just got to take off your filament run out sensor Make sure there’s no debris in there and then put it back together. This is pretty common on my ams I’ve seen about 10 times so far.
That is exactly what I had to do to my sensor housing. Filed it down on the very same corner and all is well still to this day. Spare still waiting its turn. 
It’s now happening on every single print from AMS, making AMS useless. I don’t want void the warranty by filing down the corners since it’s less than two months old.
The printers are awesome, AMS…just so so. Mine didn’t work right out of the box, had to wait 10 days for new motor and hub replacement. Now this, it has been 6 days since I filed a ticket, still no reply yet. 
Next time can you give your subject a more clear name so that others can find the thread? Something like ‘Error: Filament broken in the extruder’
Finally got the replacement senor today, as far as I can tell it’s identical component as the stock one. But the replacement’s magnetic lever doesn’t get stuck on that corner as the stock one does. Problem solved, thanks @3DTech.
Just in case BL reads this, round off those corners would prevent this issue for good. New injection tooling is costly, but it would save a lot of headaches for everyone.
