Support

You have set the $live_site in your site's configuration.php file. The non-www to www redirection (or vice versa) is not allowed as it would create a redirection loop.

For example, let's say that your $live_site is https://www.example.com and you set a www to non-www redirection. When you access your site as https://example.com the .htaccess file will redirect you to https://www.example.com. However, this does not match the $live_site. As a result Joomla itself will redirect you to https://example.com. This will cause the .htaccess code to redirect you back to https://www.example.com and so on and so forth until the browser gives up, effectively making your site inaccessible.

The same thing happens if your $live_site is using http:// but you are using the HSTS option in the .htaccess Maker.

There are two alternative solutions:

1. Do not use the www to non-www (or vice versa) redirection and the HSTS features in the .htaccess Maker.
2. Empty the $live_site in your configuration.php file, you do not need it in most cases (if you don't know if you need it then you definitely don't need it, this feature is there for some broken configurations which were rare back in the late 00s and practically non-existent in modern server environments).

I can tell you that $live_site is not exposed in Joomla's Global Configuration, so you didn't do it through that interface.

I can also tell you that if you recently restored a backup of the site the Site Setup page does have a Live Site field which lets you change the $live_site in the configuration.php. We have that option there in case you had already set it in the backed up site and you're restoring the site to a different domain — but we won't stop you from abusing it either, following the old UNIX mantra that you don't ask a user why they want to shoot their feet, you just give them the biggest, meanest gun which will shoot their feet clean off the first time they try.

If that wasn't the case, yes, it must have been an extension doing that. Doing that without your explicit consent would be a big red flag — nothing should ever change the configuration.php file unless the user is absolutely clear on what is going to happen and explicitly provide their informed consent. Any problems emanating from a configuration.php change can be, as you found out, very hard to troubleshoot unless someone who's seen that problem before tells you where to look and what to look for.