Lead Developer
It sounds like you have a plugin added that is making all links around images open a lightbox of their destination.
Good idea if the image is linking to itself or a larger image, not a good idea if it’s linking to another page as the post image does.
I would suggest letting the dev of that plugin know, as this is a bug in their plugin.
Of course, you can remove the link using this function: https://gist.github.com/generatepress/65aff21092a25e5a6f97
Adding PHP: https://generatepress.com/knowledgebase/adding-php-functions/