Editing page gives 404 not found error after 4.2.4 upgrade

Hello. I’m getting a “Not found, error 404” error when editing a page. This started after upgrading to WP 4.2.4.

The pages are there and displays fine on the site, it appears to be just an issue in the admin panel when trying to edit.

Here’s an example of a page that I’m attempting to edit – it shows fine on the site: good link

Here’s the url link I get when I click edit on that page in the admin panel – which results in the 404 error: 404 link

My troubleshooting steps so far are:

– I’ve tested out reverting to a backup on version 4.2.3 and it works fine, no issues with 404 errors on page edits.

– Upgraded to 4.2.4 and the 404 edit issue occurs.

– Disabled all plugins = 404 issue still remains.

– Changed to the default 2015 theme = 404 issue still remains.

– Went to Admin > Settings > Permalinks and clicked ‘Save Changes’ = 404 issue still remains.

Suggestions of what to try next are very welcome ! Thanks.