Do you use the WYSIWYG field to add the Modula gallery shortcode to the field value? Also, please try to add the Modula shortcode directly to the post content without using the WYSIWYG field and Oxygen builder to see if it works.
I suggest you use the WYSIWYG field, add the Modula shortcode to the field, and use the Meta Box shortcode only without the Oxygen builder. If it still doesn't work, I think the Modula shortcode doesn't work in another shortcode.
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