In some cases, if there is issue in code or whatever, and try to update the post in Gutenberg post-editor, you will get "Updating failed" error message:
Is there any way to debug/find out the reason (i.e. in console) what error happened there or what was the response from the erroneous page?
Solution
You could poke around in the Network tab. Filter the requests by XHR. You can view the headers and the Response from there.
I think I read somewhere that error reporting is something Gutenberg dev is planning on improving in the future.