When installing Sitecore Experience Commerce 9.0.2 I ran into trouble getting anything other than the carousel on the home page displaying. Nothing in the logs, I could see products in the catalog, just no navigation, footer, or products on the site. I rebuilt indexes, redeployed about 20 times only to find out the issue was with my config patch to add the storefront in as a new site (this did work in the previous version...) with a custom domain. Eventually I realised that this should have worked without a patched site definition and looked into how SXA handles multisite and there was the answer.
You can manage your sites using the SXA Site Manager that is part of the PowerShell Toolbox
Here I found that the custom domain I provided in my installation script had not carried through and it retained the existing sxa storefront URL. After I updated the domain (using the intuitively named "open" button) everything finally started working.