While developing the archive.html template file I encountered a problem where the Template Part Not Found message was displayed but there was no template name. The only attribute value passed to gutenberg_render_block_core_template_part() was tagName, with a value of div.

Analysis of the HTML comment that formed the wp:template-part block indicated that I was missing a comma between attributes.

<!-- wp:template-part {"slug":"footer-menu","theme":"fizzie" "className":"footer-menu"} /-->

It would be helpful if the error could be detected and a message produced.