Custom Block Disappearing in Gutenberg

Hi, I have the same problem, which was already reported (eg. here https://wordpress.org/support/topic/custom-block-disappearing-in-editor/). Custom block just disappears in Gutenberg (like in this video from previous poster). I do not need real-time preview, placeholder would be fine. Empty line is not 😅. We are using newest WP version, newest PHP and newest Genesis Custom Blocks (however I tried with both older WP and PHP versions)