I do. I have done some more investigating since I made my initial post, and apparently a redirect limiting extension installed in my browser was causing all of those links on the extensions page to fail (I was always ending up back at https://piwigo.org/ext/index.php).

I had forgotten that extension was even installed and had never seen this kind of behaviour on other sites so it didn't immediately occur to me to investigate that.

I apologize for the mistake.