There is something strange with the New Document Profiles.
When they contain artwork, it is not visible when you create a new document based on that profile preset.
But it becomes visible when you, in your case export as SVG using Export for Screens Asset Export. It will include the artwork from the New Document Profile.
Another example is when you drag artwork from a document based on that profile to a CC Library, it will include that artwork when you (alt) drag it into a new document.
Can you open the New Document Profile that you use for the problem documents (could be named Print.ai, Art & Illustration.ai, Web or Mobile) and check if it contains artwork?
User > Library > Application Support > Adobe > Adobe Illustrator (version number) > (your language) > New Document Profiles
Thank you so much for replying, you're a life saver! You really helped me fix my problem. Turns out, my new document profile for Web documents contained the artwork for some reason.
For anyone else with this problem, here's how to get to the files to fix it:
Go to the settings file of the most recent version of Illustrator that you're using. Just type in these addresses without the quotations to Windows Explorer or Finder
Then go to New Document Profiles and go through each Ai file on the list. All of them should be blank. The one that isn't is the one that's creating the problem when exporting as an SVG. Just delete the artwork and save. Then everything should be fine.