Getting ob_end_flush(): error

That does sound like a server issue, Have you spoken to your web hosts about it?

I realize this is late but perhaps it will help someone else If you have already resolved the problem.

I fixed that error by adding the following code in theme functions:
________________Copy and past the code below______________

remove_action( ‘shutdown’, ‘wp_ob_end_flush_all’, 1 );

________________Copy and past the above code______________

You can use a plugin such as “My Custom Functions” plugin to do it safely.
Enter this into the plugin settings while it is switched to off (Red) on the toggle switch you will see after you navigate to Plugins / installed plugins, and then click Settings on the “My Custom Functions” plugin.

Paste in the above code in the space provided there and then click Save. After you save it Then set it to ON (Green) and then click save again. Done.
Better explanation of the plugin:
On the “Main” tab, place your PHP code in the field, switch the toggle to the “ON” position and click the “Save changes” button.

In the off chance it crashes a website ( I have never had it to) but this is the instructions to fix it:

The plugin has a built-in functions for checking the custom code for syntax errors, duplicate functions names, and etc. But plugin is not perfect, so there are times when the entered custom code causes the error and white screen (WSOD). This is due to the fact that your custom code has a syntax error that this plugin could not detect. When this happens with you, please perform the following steps.

Access your server via FTP or SFTP. If you aren’t sure how usually your web hosting provider will have instructions somewhere on their website.
Browse to the directory wp-content/plugins/my-custom-functions/. Please contact your web hosting company to get help if you can’t find this folder.
Rename the file START to STOP. This will stop the execution of your custom code.
Log in to Admin Area of your WordPress website.
Go to the plugin settings page Settings ? PHP Inserter.
Edit/fix your custom code that you entered before the crash.
Return to the plugin folder and rename the file STOP to START and you’re done!

• This reply was modified 6 years, 4 months ago by stanwilliams. Reason: Fix Typo
• This reply was modified 6 years, 4 months ago by stanwilliams. Reason: minor correction
• This reply was modified 6 years, 4 months ago by stanwilliams.