Hi Inbal,
Sorry to hear of the problem you are having.
Do you mean the site works fine If you disable the Unyson plugin?
Please make sure you are using the latest version of PHP on your server by referring to the information provided in the following pages.
https://www.wikihow.com/Check-PHP-Version
http://php.net/supported-versions.php
Can you please try temporary enabling WP_DEBUG mode? To do this, just go to wp-config.php include this:
define('WP_DEBUG',true);
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.
Best regards,
Shufflehound team