Not sure what might be going on here, but after upgrading to WordPress 5.7, some posts started timing out. Viewing the post. Searching in the Posts interface for anything that was in the post. Trying to list posts that had its tags. I could search for it on the blog, but not in the admin area. Error logs on the web server showed a connection timeout. The only way I could find them was through the Search Regex plugin, and it turned out I could still edit the post. Though I couldn’t save any changes without getting the same timeout.
Both posts that I’d been alerted to had emoji in the title. Hmmm….
I tried removing the emoji from the title and saving it. The post loaded again! And I could search for keywords and tags that matched it!
Just for kicks, I pasted the emoji back in. Saved. No problem.
I don’t know what changed, but apparently older versions of WordPress were storing emoji in titles differently or something, and re-saving it fixes it?
Anyway, that seems to work, so I’m posting this here for anyone else with the same issue to see what worked for me.
Update: I checked another blog that updated from 5.6 to 5.7 and had emoji — in some cases the same symbols — in titles, but it wasn’t affected by the same problem. I’d guess it’s either a combination with some plugin, or something left over from the fact that this site has been updated continuously from some very old versions of WordPress.