Sorry, there were two things:
- Vanishing rates. MDL-26613 says "it's going to be extremely difficult to actually implement in most uses of the rating system". Fair enough.
- The "Read" posts flagged as "Not read". I think that one is more important. Was it reported too?
No idea on Amazon Linux. On Debian and derived distributions it would be '# apt-get install php-zip'.
BTW, '$ php -v' could be misleading, since Moodle is interested in the CGI version of PHP. Run phpinfo() in a php file and call it from the server to see the details of the CGI PHP.