What do I do if my WordPress site is suddenly sanitizing portions of URLs it shouldn’t?

It turns out that the folder wp-content/mu-plugins, for whatever reason, didn’t contain plugins, but instead a dump of broken copies of most pages on the site, as well as an outdated copy of the entire public_html directory, with another plugins folder nested inside of it, etc! How that happened is beyond me, but simply removing the entire folder corrected all errors on the site and actually significantly improved its performance!

Note: If you are encountering a similar issue, DO NOT use this as your go-to solution unless you are absolutely sure it is a problem: mu-plugins should normally contain critical plugins.

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