I read someone else had a similar issue so the fix that he was provided is posted here: https://generatepress.com/forums/topic/strange-php-error-in-blog-post/
What’s happening is there’s an element that’s erroring and leaving us with an error code posted three times,
“/var/www/html/wp-content/plugins/gp-premium/elements/class-block-elements.php on line 1306”
I have drafted the element “Post Navigation” on the Inbound theme and the error is gone, so this issue is there.