I ran a query created by @peterh to find all my network posts. It works perfectly for the task, but it believes that all my posts made to MathOverflow Meta were actually made to https://mathoverflow.meta.stackexchange.com, which does not exist. My subject question is "why does it think this?", but I guess my real question is "shouldn't it stop thinking this?"
That's a fault of the query, not of Stack Exchange. MathOverflow should be special-cased, right now it triggers this part of
name LIKE 'StackExchange.%'
RIGHT(name, LEN(name) - 14) + '.stackexchange.com'
That's an old query, but there are better ways to generate links in cross-site queries. I regularly run those, so I designed a solution based on a community-maintained list of sites and database names: How can I get URLs and site names for a cross-site SEDE query?