Hello,
The plugin already runs on a multitude of server configurations. It is highly unlikely that the cpu or memory is the problem. In any case, you should be able to see if your memory is exceeded by scanning your php/mysql error logs, or via some dashboard.
When you trigger the cron job manually, sometimes you get success, and some times you get a white page in your browser. This means that some times there is a PHP error. So:
1. Could you please check your logs for errors? There should be something there.
2. Also, when you get a white screen, does the browser immediately finish loading, or does it look like it is still loading for a few seconds before giving up?
3. Does the problem persist if you deactivate your coin adapter? Or is the result always success when the adapter is deactivated?
Looking forward to your reply.