@BFD Calendar Make sure you've got /site/config.php setting $config->debug = true; just so you can see errors. You may want to set it so that it's only in debug mode for your IP address, i.e.
$config->debug = $_SERVER['REMOTE_ADDR'] === '123.123.123.123';
Keep an eye on the files in /site/assets/logs/, especially errors.txt. If you have shell access, you can "tail errors.txt" in that directory to see what the latest error messages are. You don't need to be able to login to the admin to view these logs, you can just locate them on the file system. Most of the time they will reveal whatever the issue is. If it's not clear, then post the last few log entries here to see if we can identify anything from it.
The errors you mentioned may be expected, as it looks like they are trying to access something related to cgi-bin or a .well-known file, which are specific to your hosting and not to ProcessWire. So if your host blocks those addresses, then you'd expect to see this in the apache error log. Basically, I don't think those error messages are related to whatever is preventing your site from running.