Apache adds a trailing slash to something not a subdirectory

In the directory foo, I have the file bar.html, and no other subdirectories or files. I also have Options +MultiViews in my .htaccess. None of my other rules are redirects or do any rewriting.

When I try to access https://example.com/foo/bar, I expect it to access the file bar.html. Instead, it redirects to https://example.com/foo/bar/, and then rightly 404s, because there is no subdirectory bar.

This didn’t used to happen. It started happening after I accidentally made a bar subdirectory under foo. I tried to access it, realized the mistake, and then deleted it; this is when it started happening.

What can I do to diagnose this problem, if not fix it?