Hi @ufanders,
I hope you're doing well. This is unusual, can you confirm you are using the latest version of Fusion 360?
With that said the best way to fork a design is actually not to do the Save As. Here's the procedure
1) Create a new electronics design
2) Link to an existing schematic and pick the schematic you want fork. MAJOR KEY: Make sure the Save as A Copy checkbox on the bottom right is checked. This is the key to getting this to work.
3) Repeat the same thing with the board making sure to follow the MAJOR KEY.
We are working on making this better.
Let me know if there's anything else I can do for you.
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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