Setting custom domain in Github Pages consistently 500 errors

[snarfed]

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Hi all! I've successfully published a web site w/Github Pages, http://snarfed.github.io/snarfed.org/ , but when I try to set a custom domain in settings, it consistently 500s. Is this a known error right now?

Thanks in advance!

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[snarfed]

Thanks (template? AI?), but no. https://www.githubstatus.com/ shows no incidents, either with Pages or anything else. Browser cache is almost certainly not it, but I've cleared it and Shift-reloaded anyway. I haven't even gotten to DNS settings yet, this is before Github tells me the DNS records I need to add. And I've only tried this a few times so far.