There are two instances that will cause your product widget and/or your star rating widget not to show.
When you don’t have product reviews yet or when no reviews are published for the product
If you do not have product reviews, though the product widget will show an empty widget with a prompt for your visitors to leave reviews for your business, the star rating widget will not show at all.
The star rating widget only shows when there are published product reviews for the particular product.
2. When product widget is turned off. Your product reviews widget will not show when the widget is turned off.
To turn the product widget on, refer to this guide and follow the same steps.