Having to deactivate plugin to edit core files

Hi,

I have had the plugin installed for a few months now and it’s really good, however i’ve got an issue where I have to deactivate the plugin every time I want to edit any of the WP core files such as the header, footer or functions files. The error I get is:
Unable to communicate back with site to check for fatal errors, so the PHP change was reverted. You will need to upload your PHP file change by some other means, such as by using SFTP.

Cheers

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