Database Error on single site

I have a working multisite setup with about a dozen sites, some mapped to their own domains, some not. Everything is working perfectly, except one site.

It shows up in the list of sites in the network admin dashboard, and looks fine there. If I try to visit that site’s dashboard, I get shunted to the dashboard of the first site in the list. If I try to visit the site via its mapped domain, I get “Error establishing a database connection”. If I try to visit the site via its subdomain address, WordPress behaves as if I’m trying to register a new site.

The entire multisite install is using the same database, and all other sites work without issues. I can create new sites just fine.

I have not done any changes to that particular site in over a month, and it worked fine then. No new plugin installs, no updates of the plugins or themes that site uses.

I have deleted a different site that came before the broken site in the site order; I do not know if the site broke before or after this. Other sites after the deleted work fine, so I do not think this is relevant, but I’m mentioning it just in case.