Id Louis Rossman's YouTube rant is correct, nobody involved here modified the AGPLK software. They just used a version of the AGPL software from before Bambu Labs changed the auth code.

While I agree that the AGPL does not grant users any rights to Bambu's cloud service, sending DCMA nastygrams to people hosting copies on old versions of their software isn't the right (or even legal) way to enforce that. And since Bambu choose to build their products and software stack on pre existing AGPL code, they've backed themselves into a corner a bit with other options. They can add new auth to new versions of the code (which is stringer than just hardcoded useragent-like strings in the code) but they'll then have to release the source code to their new version - exactly like the original authors who chose the AGPL intended.