revisions issue with block editor

[kyborn]

Okay, I just upgraded my site to WordPress 5.0.2

I tried to edit an existing post, when I converted the contnt to block editor, the auto save kept telling me update did not happen "Updating failed", when I tried a preview, it never showed just keeps drawing he WordPress logo and "Generating preview…"

I installed and activated the "classic editor" plugin and tried to edit the edit box is totally blank!

I went back and deactivated the classic plugin then went to the post to edit but it was totally blank except for the header box and bellow a faint box with the title of "Classic"

Fortunately I found an option "Convert to Blocks" when i did that, the content re-appeared but the "preview still does not genrate.

My current theme is Twenty Seventeen Version: 1.9

I went back to the post to try to recover a previous version, but there is no revisions history and found no option to activate.

I searched the forum for help on reviosions and found * * adding line to save post revisions per WordPress

 */ https://codex.wordpress.org/Revisions 
 */ and at https://codex.wordpress.org/Editing_wp-config.php#Post_Revisions
 */

I have edited wp-config with these lines, I am guessing I have o log out close the browser and revisit the site for that code change to activate. I have no idea what to do from there.

[SergeyBiryukov]

Related: #45744