Fatal Error: Out of Memory

try increasing memory available for php.
There are also, numereous threads that deal with this topic. For example: https://www.ads-software.com/support/topic/fatal-error-allowed-memory-size-6

I am assuming you are saying the php_memory_limit is 256 from your php info file on your account?

Some shared web hosts allow you to set your own php memory limit yet if it is a shared system those resources may not always be available for your site to use.

I definitely recommend trying increasing the memory via the wp-config as linked by Tara above. Also check into increasing your memory limit via php.ini on your web host.

You can see my memory limit increase via php.ini at the following link:

[ Link redacted, please use Codex links when possible ]

https://codex.www.ads-software.com/Editing_wp-config.php#Increasing_memory_allocated_to_PHP