Three causes, in order of likelihood:
Your free trial ended without a paid plan. All published products are automatically unpublished (they look like they vanished from your store). Your selections are saved: subscribe, then toggle Publish to Store back on in My Products.
Your store isn't connected. Check Connect Store for green Connected; reconnect if needed, then toggle Publish to Store off and on.
Neither? Email [email protected] with the product names and a screenshot from My Products.
Separate issue worth ruling out: if products exist in Shopify but nobody can see your store at all, it's Shopify-side storefront visibility (a password-protected or unpublished store), not syncing.