I feel like it’s worth mentioning that importing GCode into MillMage isn’t a recommended way to work. You can run the GCode from MillMage, which is effectively using it as a gSender replacement - if you did that, it would run fine.
You seem to be trying to import the GCode files, expecting some reasonable representation of whatever is in there, and MillMage was never intended to work this way.
The GCode import in MillMage was created as a way to debug and valide our own GCode output, just so I can see if the shapes exported match what I expect.
If you create GCode elsewhere, run it like you would from gSender, don’t import it.
If you’re trying to recreate the paths in a GCode file so you can use MillMage to rebuild the GCode, we’re working toward that, but it’ll be a “best effort”.