Eric Beiler, thanks for the follow-up. I see that your site render fine now without 404.
Copying your comment from your other thread : *"So it looks like the custom domain finally deleted through the script after several tries -Maybe I did not wait long enough. It looks like the custom domain was finally deleted."
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My colleague SnehaAgrawal-MSFT had shared suggestions via PowerShell script to delete custom domain of static web app.