In order for an app block to appear on a product page you must actually render the block.
We see many themes that allow you to add an app block to the page but the code itself never renders the app block
Option your product template liquidfile that contains product content. Typically product-tempalte.liquid or product-main.liquid.
Search for a {%- for block in section.blocks -%}
and or for:
{%- case block.type -%}
Inside thie case statement you need to add the following code:
{%- when ‘@app’ -%}
{% render block %}
This code will render the app block.