Does anyone have an idea why a query variable would make it into the page query for some rewrite rule matches, and not others?

Two different URLs, the correct rewrite rule is matched in both cases, and the correct query strings are generated. But with one URL page_id isn't included in the query, so the page isn't found, while with the other URL it is included and the page loads properly.

I'm using the Query Monitor plugin to try to debug this: wordpress.org/plugins/query-monitor

Prob not a good question for the stack - Can you tell me, did the wordpress.com/plugins function break? Until a month or so ago, I could manage plug-in updates from the one page for multiple blogs. That now comes up with "loading my sites" but never finishes.

I figured out my issue. I had a misbehaving callback that was forcing a 404 to be thrown.

Never mind. I signed out and back in. I am back in business.