“Unexpected output” alert

The format of the output looks correct. Maybe it is truncated by an other plugin that buffers and modifies all output. I have seen that before, but i do not remember what plugin it caused (it could be fixed in that plugin to disable output buffering, if that makes sense to you…)

If you can give me a list of your other active plugins, i can say more.
Also you could disable them one by one, any kind of optimizing plugin could be suspicious.

For the time being, you could disable ajax by setting Advances settings -> System -> I -> Item 5: Ajax method to Frontend none… (3rd choice), but that will degrade user experience.

Thank you for the quick answer. I know about output buffering, but I wouldn’t know offhand which of the installed plugins interferes with the gallery page.

At the moment we have:

• Adminimize
• Advanced Woo Search
• Akeeba Backup Core for WordPress
• Better Search Replace
• Classic Editor
• Classic Widgets
• Clean Image Filenames
• Contact Form 7
• Disable Visual Editor WYSIWYG
• Duplicate Page
• Foobox Image Lightbox
• HTML Editor Syntax Highlighter
• Huge IT Slider
• Image Widget
• Loco Translate
• No Right Click Images Plugin
• Widget Visibility Without Jetpack
• WooCommerce
• Woocommerce Products per Page
• WP Featherlight
• WP Photo Album Plus
• WP Statistics
• Yoast SEO

It’s a bit messy here, was an apprentice project, sorry for that. ^^’

I found a wppa-theme.php in the theme directory – first assumption was that this is responsible, but that was not the case. Afterwards I tried a step-by-step deactivation of plugins but still no success..

Finally, I found this little script in the child theme:

jQuery(document).on('ready', function(){
	function isEmpty( el ){
		return !jQuery.trim(el.html())
	}
	if (isEmpty(jQuery('.wppa-box-text'))) {
		jQuery('.wppa-box-text').remove();
	}
});

? Deactivated and now it works. Somebody didn’t know how to hide stuff with CSS obviously. ??

Thanx for this explanation! And nice you found it.