My website is private (login required) so i cannot provide a link. Here is the code for a simple three columns with embedded paragraph blocks. When displayed, instead of columns horizontally, the columns are displayed in vertical rows.
<!-- wp:columns {"columns":3} -->
<div class="wp-block-columns has-3-columns"><!-- wp:column -->
<div class="wp-block-column"><!-- wp:paragraph {"backgroundColor":"pale-cyan-blue"} -->
<p class="has-background has-pale-cyan-blue-background-color">Column 1</p>
<!-- /wp:paragraph --></div>
<!-- /wp:column -->
<!-- wp:column -->
<div class="wp-block-column"><!-- wp:paragraph {"backgroundColor":"vivid-red"} -->
<p class="has-background has-vivid-red-background-color">Column 2</p>
<!-- /wp:paragraph --></div>
<!-- /wp:column -->
<!-- wp:column -->
<div class="wp-block-column"><!-- wp:paragraph {"backgroundColor":"luminous-vivid-amber"} -->
<p class="has-background has-luminous-vivid-amber-background-color">Column 3</p>
<!-- /wp:paragraph --></div>
<!-- /wp:column --></div>
<!-- /wp:columns -->
