preview in customizer doesn't work

Often times, this is due to a plugin conflict. I would recommend temporarily deactivating all plugins on the site to see if this fixes the issue.

If it does, you can then reactivate each plugin one-by-one until you find the source of the issue. Deactivating the plugins like this won’t have any affect on their settings.

I tried, but deactivating the plugins doesn’t change it. It appears with activating the founder theme.

By the way: This happens only live but not on my local system. I did a backup of the live system and installed it on my local system: the preview works.

Do you have another idea? It’s not a big deal if you don’t. I find it just irritating and not so very important, really.

Okay thanks for trying that.

The next step is to make sure that both Founder and WordPress are on their latest versions.

Founder: 1.23
WordPress: 4.4.1

If either are below their latest version, please update and check the Customizer once more.

If this doesn’t work, try re-saving your Permalinks settings. This will cause WordPress to rewrite the .htaccess file and rule out any file corruption errors with it.

Lastly, if none of these steps works then a PHP error may help locate exactly what the source is. You can find your PHP error log in your host’s cPanel, or in your WordPress dashboard after installing Error Log Monitor.

Just for the record:
I tried your suggested solutions without success. But I moved the website from my test system to my live system and the error didn’t occur again.

Got it, thanks for sharing that here. I’ll look into any issues with the theme that may cause a conflict with local setups.