When you check the error logs, you can see many things.

Some things you can ignore:

Web browsers, search engines and robots sometimes look for these files, but these files are optional and nothing bad happens when they cannot find them.

• robots.txt is optional and is used to tell search engines and robots whether you want them to visit or not. If the file does not exist, it is the same as saying everyone is welcome.
• favicon.ico is an optional 16 x 16 pixel icon file and if it exists, most modern web browsers will display the icon when mentioning your web page (such as in a tab or in a favorites menu).
• 500.shtml and similar files are used for custom error messages.

Some things you can fix:

The file is either in the wrong place or needs to be republished. Be sure that all of your files and folders are uploaded inside the public_html.

This is the most common 403 error. We can help you fix this.

This is the most common 500 error. We can help you fix this.

This can be fixed by adding executable permissions [755] to the file.

This means there is something bad in the .htaccess file. Perhaps there is a php_flagline needs to be deleted.

Possibly this is a perl script and needs to say  #!/usr/bin/perl -w  on the first line.