“Failed to Open Stream”

See if this helps:
https://www.wpbeginner.com/wp-tutorials/how-to-fix-the-wordpress-failed-to-open-stream-error/

It helps me somewhat understand the first warning – is this “wp-includes/class-wp-query-update.php” missing/failed to open?

However, I’m unclear what it is and what I need to do to fix it.

It explains under heading "Fixing Failed to Open Stream Error in WordPress"

• This reply was modified 6 years, 2 months ago by t-p.

I still don’t understand – it feels like a different language to me.

If it is a plugin or theme file, then this means that the plugin or theme files were either deleted or not installed correctly. Simply deactivate and reinstall the theme / plugin in question to fix the error.

I don’t think the file in question is a theme or plugin? I’m not sure – I have no idea what a .php is!

However, it is also possible that WordPress is unable to locate the files because of a missing .htaccess file in your root folder. In that case, you need to go to Settings ? Permalinks page in your WordPress admin and just click on the ‘Save changes’ button to regenerate the .htaccess file.

I can’t log into my WordPress admin site, so I’m not sure how this step can help me.

If the error message is followed by ‘Permission denied’, then this means that WordPress does not have the right permission to access the file or directory referenced in the code.

I don’t see permission denied in the message.

Lastly, some WordPress plugins load scripts from third-party sources like Google Analytics, Facebook APIs, Google Maps, and other third-party APIs.

Again, I don’t know if the file in question falls under this category?

Any very elementary, step-by-step advice specific to the messages I received would be greatly appreciated.

Thanks!
Jen

I can’t log into my WordPress admin site

Try:

manually resetting your plugins (no Dashboard access required). If that resolves the issue, reactivate each one individually until you find the cause.

If that does not resolve the issue, access your server via SFTP or FTP, or a file manager in your hosting account’s control panel, navigate to /wp-content/themes/ and rename the directory of your currently active theme. This will force the default
theme to activate and hopefully rule-out a theme-specific issue (theme functions can interfere like plugins).

If above steps don’t help try – MANUALLY updating. Download WordPress again and unzip it. Access your server via SFTP or FTP, or a file manager in your hosting account’s control panel (consult your hosting provider’s documentation for specifics on these), and delete then replace your copies of everything on the server except the wp-config.php file and the /wp-content/ directory with fresh copies from the download. This will effectively replace all of your core files without damaging your content and settings. Please read the Manual Update directions first.

Backup: If you haven’t already done, always backup everything (including your database) before doing any actions, just in case something really goes wrong. You can never have enough backups!