Critical Error On Featured Content Breaks Site

So ... If I am in a browser and I view a featured content page that I have created and then I use the 'back button' on the browser (any of them - FF, IE, Safari, Opera or Chrome (and I have all these installed and the latest versions)). Then the whole featured content system breaks. I get this error message. So the error is as follows ... POST ERROR e@http://raysphotos.uk/wp-includes/js/dist/media-utils.min.js?ver=1.2.4:1:5052 Ag@http://raysphotos.uk/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:63:107 Vg@http://raysphotos.uk/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:89:442 ph@http://raysphotos.uk/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:217:70 lh@http://raysphotos.uk/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:126:411 O@http://raysphotos.uk/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:121:71 ze@http://raysphotos.uk/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:118:14 mg/<@http://raysphotos.uk/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:53:49 unstable_runWithPriority@http://raysphotos.uk/wp-includes/js/dist/vendor/react.min.js?ver=16.9.0:26:340 Ma@http://raysphotos.uk/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:52:280 mg@http://raysphotos.uk/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:52:498 V@http://raysphotos.uk/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:52:431 Sb@http://raysphotos.uk/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:213:96 Mg@http://raysphotos.uk/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:85:82 t@http://raysphotos.uk/wp-includes/js/dist/data.min.js?ver=4.9.2:1:19198 Tt/</e<@http://raysphotos.uk/wp-includes/js/dist/data.min.js?ver=4.9.2:1:19283 o/<@http://raysphotos.uk/wp-includes/js/dist/data.min.js?ver=4.9.2:1:15212 o@http://raysphotos.uk/wp-includes/js/dist/data.min.js?ver=4.9.2:1:15184 K/y</<@http://raysphotos.uk/wp-includes/js/dist/data.min.js?ver=4.9.2:1:13576 p@http://raysphotos.uk/wp-includes/js/dist/data.min.js?ver=4.9.2:1:6765 a/</</<@http://raysphotos.uk/wp-includes/js/dist/redux-routine.min.js?ver=3.6.2:1:9535 I/</<@http://raysphotos.uk/wp-includes/js/dist/data.min.js?ver=4.9.2:1:8752 A/</</<@http://raysphotos.uk/wp-includes/js/dist/data.min.js?ver=4.9.2:1:9187 dispatch@http://raysphotos.uk/wp-includes/js/dist/data.min.js?ver=4.9.2:1:8484 i/<@http://raysphotos.uk/wp-includes/js/dist/redux-routine.min.js?ver=3.6.2:1:9181 e/<@http://raysphotos.uk/wp-includes/js/dist/redux-routine.min.js?ver=3.6.2:1:5078 e@http://raysphotos.uk/wp-includes/js/dist/redux-routine.min.js?ver=3.6.2:1:5053 u/<@http://raysphotos.uk/wp-includes/js/dist/redux-routine.min.js?ver=3.6.2:1:5007 POST TEXT <!-- wp:separator {"color":"yellow"} --> <hr class="wp-block-separator has-text-color has-background has-yellow-background-color has-yellow-color"/> <!-- /wp:separator --> <!-- wp:columns --> <div class="wp-block-columns"><!-- wp:column --> <div class="wp-block-column"><!-- wp:image {"id":1282,"sizeSlug":"large","linkDestination":"custom"} --> <figure class="wp-block-image size-large"></figure> <!-- /wp:image --> <!-- wp:paragraph --> <p>DUXFORD</p> <!-- /wp:paragraph --></div> <!-- /wp:column --> <!-- wp:column --> <div class="wp-block-column"></div> <!-- /wp:column --> <!-- wp:column --> <div class="wp-block-column"></div> <!-- /wp:column --></div> <!-- /wp:columns --> This theme is driving me up the wall!