Shop page doesn’t show any products

Hi,
In one of the site I build, there is a strange bug.
I defined a shop page in the settings, but when I view the page I don’t see any products. however, if I view the archive page, I can see the products.
I debug this, and saw that the global variable $product in the file content-product.php is null when accessing this file through the shop page. This behevoir doen’t occuer by accessing the file through proudcts archive.

Any idea what’s going on?