Error on logo in SDTT

You appear to load an additional external Stylesheet

<link rel="stylesheet" href="https://www.inexhibit.com/wp-content/plugins/sitepress-multilingual-cms/res/css/language-selector.css?v=3.3.6" type="text/css" media="all" />

This one is not allowed.

Not sure, but you are using an external CSS file that isn’t allowed…

For the logo issue, you can add a site icon.

Thank you for your support Omeprazot!

This is the css which stylizes the language selector installed by the WPML multilanguage plugin, it would be quite strange that it could interfere with the publisher logo JSON-LD markup.
I’ll try to tweak it a bit and see what happens.

Thank you Mohammad!
Maybe I am wrong, but I guess a square image is not allowed as publisher logo in rich snippets
https://developers.google.com/structured-data/rich-snippets/articles?hl=en_GB

Dear Mohammad,

It took me some time to make a try and… you were completely right!
I added the site icon through the WP dashboard, and…voilà, now the error in GSC for the AMP pages is fixed. The site logo included in the JSON-LD code for the non-AMP pages remained unchanged, while the site icon has become the logo for all the AMP-enabled pages.

Thank you so much for your beautiful work and kind support!

What I wrote before is only partially true.
The problem with the Structured Data Testing Tool is gone, yet the page does not validate for AMP due to the problem remarked by Omeprazot.
This issue is nor related to the logo property, but to the stylesheet call made by WPML. I know this problem is well-known (see https://github.com/Automattic/amp-wp/issues/43) yet still not resolved. Do you know some solution / workaround for this?

Ok, solved by adding “define(‘ICL_DONT_LOAD_LANGUAGE_SELECTOR_CSS’, true);” to functions.php