Sorry to hear of the problem you are having.
Can you please try temporary enabling WP_DEBUG mode? To do this, just go to wp-config.php include this:
You might already have a line for WP_DEBUG, so just make sure it’s set to true.
Let me know what errors if any you are getting when you face this issue.
Also please make sure you are using latest version of PHP on your server by referring the information provided in the following page.