Appearance>Editor – CANNOT EDIT

The Problem:

I am unable to make changes in the WordPress editor: Appearance>Editor.

Details:
I am attempting to add php code beneath the header of my site on a specific page. From my WP account, I go to “appearance” on the left hand side of the page. Then I move the mouse down to “editor”. After I’ve clicked on editor, on the right-hand side under “theme files”, I click on “header php” and all of the header php shows up. I know exactly where I need to paste the new code, however, when I do that and then save changes I receive this 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.”

What I did:
In order to trouble-shoot the issue I literally went through and deactivated and reactivated every active plugin just to see if one of them was somehow causing this issue, however that effort made no difference as I still received the same error.
I also cleared all of my browser cache and even tried to make the changes in another browser entirely.

What others say:
I am NOT the only person having this problem. Many other people have been having the same issue which seems to most often be associated with this latest version of WordPress – 4.94. People are receiving the same error message when trying to make changes in the editor. Most people will tell you to go ahead and try deactivating and reactivating each plugin while checking to see if doing so will allow you to make changes in the editor. This method has worked for some, but not for others – not for me.

Please, if there is any way that I can override or bypass this issue – Let me know

Thanks a million

Michael