> Add define ( 'QA_CACHE_DIRECTORY', 'cache'); In qa-config.php
There is issue with this command, it means your cache dir is inside q2a instance. It needs to be outside.
Lets says your q2a website is in dir /var/www/public_html/myqa, then create cache dir in /var/www/myq2acache, this dir will be at public_html level.
Then in change below line to
define('QA_CACHE_DIRECTORY', '/var/www/myq2acache/');
It should work. let me know if you still face issue.