WordPress users are reporting that the editor is not working as it should after updating to 5.9. In some cases, attempts to edit a post or page throws errors.
WordPress 5.9 editor issues after update
The most common problem reported by users who updated to WordPress 5.9 is being unable to edit posts or make changes and the editor encountering an unexpected error.
After doing our checks, we discovered that most WordPress websites are working well after updating to 5.9 even without any theme update.
A few of the websites that have issues with the editor not working after 5.9 update are those with heavily customized theme post layouts or those using block plugins.
Fixing editor issues after updating to WordPress 5.9
The solutions provided below cannot address all the editor issues but a number of users will find them helpful in troubleshooting their editor problems.
Solution 1: Find plugin or theme conflict
You first need to find out whether it is a plugin or theme conflict. Therefore, disable all plugins, and switch to the default Twenty Twenty-One theme. If there are no errors when using the editor, then enable your plugins one by one to identify which plugin or theme is the source of the problem
Solution 3: Plugin fixing
If you are using a plugin that comes with custom blocks like genesis blocks, then try disabling the plugin. If the error goes away then contact the plugin developer for an update.
Solution 4: Theme fixing
If you are using a theme that is built with Elementor or with custom Gutenberg post blocks like SmartMag theme, then make sure that you have updated it to the latest theme version or contact the theme developer for an update.
Solution 5: Rollback WordPress
If you have not been able to identify the problem or have identified the cause of the problem, then you can revert WordPress to the previous version as you wait for the theme or plugin to be updated for 5.9 compatibility (Here is a simple procedure on how to rollback WordPress version).