The "PHP Fatal error: Allowed memory size of X bytes exhausted" error in Drush indicates that a PHP process initiated by Drush has exceeded the allocated memory limit.
This can occur during various operations, such as clearing caches, running updates, or importing content, especially on sites with numerous modules, complex data, or demanding administrative tasks.
There's two solutions to bypass this issue; increase the php memory limit in the php configuration file or set the memory limit as parameter when executing the php drush command.