Reviews on Ryviu sometimes appear, sometimes not on your Shopify Warehouse theme. Please follow this instruction to solve it.
Log in to your Shopify store admin
In Online Store > Themes > click Actions > Edit codes
Open theme.liquid file, search this line of code {{ content_for_header }}
Move {{ content_for_header }} after <head> look like this
<head>
{{ content_for_header }}
Click Save button and go to your product page reload and check again.
I hope this helps!
All best wishes,
Ryviu team