I'm not however convinced they are really in violation by calling a binary plugin. GPL itself does not forbid you from dynamically linking to or calling unrelated software. The network plugin is analogous to a device driver, it's not core part of the slicer.
GPL differentiates between a "Combined Work" and an "Aggregate":
> A compilation of a covered work with other separate and independent works, which are not by their nature extensions of the covered work, and which are not combined with it such as to form a larger program, in or on a volume of a storage or distribution medium, is called an "aggregate" if the compilation and its resulting copyright are not used to limit the access or legal rights of the compilation's users beyond what the individual works permit. Inclusion of a covered work in an aggregate does not cause this License to apply to the other parts of the aggregate.
If they tried to add DRM to Bambu Studio and prevent you from replacing their blackbox with a different one then that would be where they would clearly go against the v3's TiVo provisions.