When I click “Customize” instead of seeing the web site in the right frame, I see the following:
Fatal error: ob_end_flush(): Cannot use output buffering in output buffering display handlers in /home/mcm2/public_html/wp-includes/functions.php on line 3720
I have the CVIT Child Theme active. Same thing happens with the CVIT theme. When I change it back to the Twenty Seventeen theme, the error goes away and the web site is displayed in the right frame as expected.
FWIW, clicking Save & Publish does work, I just have to open the site in a different tab/window.
How do I get rid of this error?