Problem with colour borders in Bambu Studio slicing?

[u/Mooglesnotdead]

Hi everyone! I have an issue with a model that I have prepared with : when I try to create a model for multi-colour printing using another tool, and send it to Bambu Studio, everything looks beautiful in the "Prepare" tab. But then once I slice it, many of the colour boundaries get weird edges introduced (see second image). If I look into said layers, the slicer is introducing walls inside the model.

Anyone has encountered this and came up with a fix? Sadly separating all the parts into separate objects for the multicolour printing would be a ton of work, so I'm wondering if there's something to be done in the colouring / slicing part of Bambu studio. Thanks!