Hi @silvio3105,
The board outline should be on the board outline layer, not sure if that's your case. The milling layer really is meant to be used for internal cutouts or unusual drill shapes. So for what you are doing here you really want to draw it on the board outline.
Additionally, you can't leave the little segment of the outline there, if you leave it you no longer have single contour and the board shape is not detected correctly. If you can correct those two things, you should get the outline you are expecting.
Best Regards,

Jorge Garcia
Product Support Specialist for Fusion 360 and EAGLE
Kudos are much appreciated if the information I have shared is helpful to you and/or others.
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