I have a site that was built with Pro that I took over from someone. From time to time there is another guy that seems pretty clueless who works on the site.
As such they built the ‘blog’ archive page outside of Cornerstone as a page utilising another plugin. After migrating the ‘blog archive’ disappeared. When I investigated the issue the migration had replaced all the code in the page with empty cornerstone html.
Essentially what started like this:
<!-- wp:ultimate-post/post-grid-parent {"cId":"<ins>7c15c193</ins>-<ins>1c6e</ins>-<ins>425f</ins>-<ins>9e90</ins>-<ins>081999f44f14</ins>","postId":"5208","currentPostId":"5208","grids":"[{\u0022blockId\u0022:\<ins>u00223faad3</ins>\u0022,\u0022name\u0022:\u0022ultimate-post_post-list-2\u0022}]","pagi":"[\u0022ultp-block-<ins>1a0189</ins>\u0022]"} -->
Ended up like what you see in the image.