Unfortunately it means opening it up again but I had it happen when about 1cm of filament broke off down where the 4 PTFE tubes come together at the bottom of the AMS unit in the path of the filament detector. I think that’s why it just reports the error before trying anything.
I opened that 4 to 1 thing to find the filament. You may be able to just use a piece of filament to push the short bit out without opening the mechanism. I didn’t try that. Be careful of tiny parts if you open and see the bambu wiki.