My site keeps sort of timing out with

This page isn’t working mysite.co.uk is currently unable to handle this request.
HTTP ERROR 500

This is mainly when I am doing something rather intensive such as exporting products using

WooCommerce – Store Exporter

It seems to happen after about 30 - 45 seconds and I cant figure out why

Here are my php.ini settings:

maxexecutiontime = 600000
maxinputtime = 60000
maxinputvars = 2000
memory_limit = 768M

Any ideas, I have confirmed these settings with <?php phpinfo(); ?>

Any ideas would be great