Whenever you come across a WordPress error one thing you should clearly remember, what would have happened before the error? What I did wrong? Have I deleted, Installed, enable or disable any plugins? Have I updated any plugins, themes or WordPress itself before the error starting to reflect?
Yes, these are very important questions to dig out the real error, if you are experiencing the following error
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
While you try to make changes in your PHP files such as header.php or footer.php or functions.php.
The WordPress wouldn’t let you make changes and throw the above error, so you are stuck.
As I said earlier try to recall what changes you have made before this error then you will reach the bottom of your error.
The major Issue
Remember, if you WordPress was running all good before the error, updating WordPress or theme would not affect much, almost 80% of the WordPress errors come from the conflicting plugins. Yes, I have witnessed all the WordPress errors coming from plugins during the last 5 years, so try to fix it this way.
Mainly there are plugins which are poorly coded and always try to influence other WordPress functionality these plugins are security plugins, captcha plugins, spam control plugins, caching plugins and some others, look for these type of plugins if you have installed on your WordPress.
If you have a lot of plugins installed on your WordPress try to deactivate all the plugins one by one and try editing the WordPress PHP file and see if the error has gone, or turn off all the plugins and then try editing PHP files. Hopefully, you will fix the issue and identify the culprit plugins causing the issue.
If you cannot fix the issue by disabling all the plugins then make sure you have cleared the cache of your WordPress, sometimes the error is gone but you still see it because of the cache, try to clear your domain cache from cpanel or ask your web host to clear the cache for your domain after disabling all the plugins. Now you should be able to make changes to your PHP files.
If the problem still persists after conducting the above two steps, do it another way around, sometimes WordPress plugins that you deactivate from admin panel are not fully deactivated. To solve this problem, log in to your cpanel and navigate to file manager, go to public_html or the folder where your site actually resides, go to wp-content>Plugins folder, you should be able to see the folders of all plugins inside this folder.
Now disable all the plugins by renaming all of them one by one, for instance, you have “Akismet” plugin installed rename this folder to “Akismat.bk” renaming it will disable it completely.
Do this to all your plugins by adding .bk at the end of each plugin folder, once you rename all the plugins, clear the WordPress cache again.
After that try to make changes in your WordPress header.php file to see if the changes are being saved. You should be able to do that now, there is no reason now for anything to conflict with it, but in case you still not able to make changes contact your host and tell them the issue, there might be a server side issue with it.
You can also make changes in your WordPress PHP files via cpanel>file manager, locate your PHP file by navigating to public_html>wp-content>themes>your theme> and locate the file which you wish to edit.