My problem turned out to be that a piece of the left side push connect internal metal collar had broken off, fell down and stuck to the magnetic sensor. I only discovered this after removing the sensor as shown in the youtube video: Bambu Lab Left Filament Sensor Replacement Guide. I can only assume that the small metal piece broke off because lately, I’ve been switching between directly feeding TPU into the extruder and using the AMS. Lesson learned! I’m thinking about splicing into the tube to insert a straight connector so that I don’t have to keep removing the connection at the print head. Either that or purchase the TPU assist module.