Sounds scary, I know, but it is super easy to fix!
​VERY IMPORTANT TIP: Copy and paste your file because you will lose text editing capabilities
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Select everything in the artboard > Go to object (Menu top bar) > Select Expand Appearance > Click Ok > Go to Object (Menu top bar) > Expand > Click ok
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Now you can save and all will be right in the world.
Here is a video to show you how to fix this problem if my instructions are not guiding you accurately: https://youtu.be/IYOhsRUaBWU