Thanks for your response, and sorry I didn’t find that page myself. I did look, but I guess I missed it.
I tried everything listed on the page. I hit save on Admin > Settings > Permalinks. I already know the items exist (these custom types are the primary content of the site). And I copied/pasted the Yoast rewrite rules to .htaccess. I did not restart the server, but I don’t think I need to for that; WordPress is not in a subdirectory so I copied it verbatim.
None of that helped, unfortunately. I also tried turning on one of the custom types but not the other and changing the max entries per sitemap to 500 instead of 1000. The sitemap index adjusts properly in both cases, but the .xml links for the custom post types just redirect to the home page (the set behavior for 404 on this site).
Any other ideas? How does it handle custom post types?