The editor has encountered an unexpected error

after updating to version 5.9

Did the upgrade perform without issues?

Yes it all went well no issues reported after the update, I have cleared my browser history, cache etc. the reopened the admin module, I can see everything on the dashboard page, and on all other items, but when I click on the allpages link I can see the list of all the pages in my site but as soon as i click on the eidt link for any of the pages I get a blank page with the error:-
`The editor has encountered an unexpected error.
Attempt Recovery – link – this appears to do nothing
Copy Post Text – link – this copies the post but not any of the images
Copy Error` – link – this copies the errorihave pasted it below:-

TypeError: Failed to execute 'appendChild' on 'Node': parameter 1 is not of type 'Node'.
    at se (https://out-of-the-box.org/wp/wp-includes/js/dist/rich-text.min.js?ver=a3e3616311fad456179e52a7528ec7fd:2:21283)
    at ae (https://out-of-the-box.org/wp/wp-includes/js/dist/rich-text.min.js?ver=a3e3616311fad456179e52a7528ec7fd:2:20218)
    at ge (https://out-of-the-box.org/wp/wp-includes/js/dist/rich-text.min.js?ver=a3e3616311fad456179e52a7528ec7fd:2:21723)
    at he (https://out-of-the-box.org/wp/wp-includes/js/dist/rich-text.min.js?ver=a3e3616311fad456179e52a7528ec7fd:2:22161)
    at x (https://out-of-the-box.org/wp/wp-includes/js/dist/rich-text.min.js?ver=a3e3616311fad456179e52a7528ec7fd:2:33710)
    at L (https://out-of-the-box.org/wp/wp-includes/js/dist/rich-text.min.js?ver=a3e3616311fad456179e52a7528ec7fd:2:34956)
    at https://out-of-the-box.org/wp/wp-includes/js/dist/rich-text.min.js?ver=a3e3616311fad456179e52a7528ec7fd:2:36207
    at https://out-of-the-box.org/wp/wp-includes/js/dist/compose.min.js?ver=058697a4c5024045c81954f411ff6dba:2:6078
    at A (https://out-of-the-box.org/wp/wp-includes/js/dist/compose.min.js?ver=058697a4c5024045c81954f411ff6dba:2:9347)
    at https://out-of-the-box.org/wp/wp-includes/js/dist/compose.min.js?ver=058697a4c5024045c81954f411ff6dba:2:9803

Any ideas?

Unfortunately no solution, but I am having the same problem for some days now (maybe due to the WP Update to 5.9 some days ago):

Things I found as possible solutions but that didn’t seem to solve the problem so far were:

-updating browser
-cleaning browser cache
-cleaning wp cache
-disactivating all installed plugins
-using troubleshooting mode of site health plugin

When Installing and selecting classic editor I can access my pages in classic editor. However when changing back to block editor the error re-appears.

Any additional ideas?

As I think this might be relevant: I am using twenty-twenty theme

We are using WEN associate Pro, we have also completed all the same things that you listed, and as yourself have had no luck.

How were you able to change back to classic editor, I can’t see any options on my page when I select a page to edit, I can only see screen options at the top level where all my pages are listed

Changing back to classic editor worked by downloading the “classic editor” plugin and the via settings -> writing -> Editor style

I also think I figured out what my problem was/is.
I am using images in some H1s of my pages (so the actual h1 is something like which WordPress 5.9’s block editor does not seem to allow (due to… reasons).
I think I’ll hope for an update/patch and stick to the block editor so far as I do not want to change the entire site appearance due to this issue.
Is this the same in your case? i.e., are you also having images as H1

best