Hi,
The changes for that feature are in the file plugins/system/hikashopmassaction/hikashopmassaction.php
So you can download the install package of the latest version and replace that file with the file back/extensions/plg_system_hikashopmassaction/hikashopmassaction.php from the install package and you should be able to use that feature.
You can also manually add these translation keys as overrides:
Code:
ACTION_PHP_CODE_IS_WRONG="Action PHP code is wrong: %s"
RUN_PHP_CODE="Run PHP code"
