I am presently writing this in WordPress, the Gutenberg editor with blocks. No problem so far, hmm, let me try to save this…. and it worked! I have three blogs, a personal, genealogical and business one. Yesterday this error started showing up on my personal blog: “Publishing failed. Error message: The response is not a valid JSON response.” Panic!
I had written the entire essay in WordPress as normal but without the ability to publish it, I had to save it on my computer until I figure out the problem. Thus, problem 2. You cannot copy an entire post if you are using the block editor. You have to copy each block separately.
Then I started googling the error message. First, I found a number of posts about checking your plugins, regenerating your .htaccess file. Made quite a mess of my blog trying to put all those into action. I uploaded all the files for the newest WordPress version in case an update had gone wrong.
More googling and then hit upon some posts about the Gutenberg editor being the root of this. The Gutenberg editor is the new WordPress block editor that came into being in 2017. I was an early adopter and hadn’t looked back, thinking this was the future. Well, when the future has a bug….
I actually don’t care for the editor; I just work with it as returning to the old editor requires a new plugin called the Classic Editor. I had actually installed a different WYSIWYG editor as I don’t like the one the Classic uses. So I let it go.
But it is the editor that’s creating this issue now and here’s how to fix it easily.
Install the classic editor plugin. That’s it! You can also make that the default editor for all uses as you will find you have a choice Settings > Writing.
Thanks to this post (it does have a bit more info) for the explicit info and the above graphic: https://passionwp.com/response-is-not-a-valid-json-response-error/