Hi Simon,
Thanks for writing in! I see that you have couple of licenses, but I could not locate the site URL as you may have set it up under different staging site. We have pushed several update releases with some fixes, so could you please make sure that you’re using the latest version by referring to our changelog (https://theme.co/changelog/).
One of the possible issues could be that either you’re using an older version of PHP or you may running out of your PHP memory limit.
Please check the PHP version running on your server and update it to at least PHP v5.6.x or higher to avoid incompatibility issues. If you’re still having this issue, try updating your memory limit by following this guide (https://theme.co/apex/forum/t/troubleshooting-increasing-php-memory-limit/16935).
Let us know how it goes.
Thanks!