Google could not open your product's landing page. Usually a draft product, a broken URL, or a robots.txt block.
Google tried to open the landing page linked from one of your products and could not load it, or the product had no landing page link at all. Merchant Center groups this family of problems under several item-level issue codes, including Product page not accessible, Landing page error, Page not crawlable, and separate desktop and mobile crawl-error variants. All of them mean the same thing to a shopper who clicks your ad or free listing: an error page instead of your product.
On a Shopify store, this almost always traces back to one of a few causes:
robots.txt disallows Googlebot or Googlebot-Image from crawling product paths.yourstore.com/robots.txt and make sure it allows both the Googlebot and Googlebot-Image user agents on product paths.Feed Doctor's deterministic rule engine checks every disapproved product for the exact conditions above: a Shopify status of Draft, no Online Store URL at all, or one of Google's landing-page/crawl-error codes, while the product is still published to the Google channel. When that combination is true, Feed Doctor automatically proposes removing the product from the Google channel, because a page Google cannot load will never sell and will keep collecting disapprovals. On a paid Shopify plan this fix can be applied automatically; on the free scan it is flagged so you can either repair the landing page and keep selling it, or remove it yourself.
Feed Doctor cannot make an unreachable page reachable. It cannot edit your theme, your hosting, or your robots.txt file, that repair is always yours to make. What it does is stop a broken link from sitting on your Google channel unattended, and it will catch the same product again on your next scan if the page is still broken.
Google's crawler and your browser can see different things. A password-protected storefront, a robots.txt rule, or a firewall that blocks Google's crawler IP ranges can all hide a page from Google while it loads normally in your browser.
Shopify's sales-channel status and your Google feed status are not automatically linked. A product can remain published to the Google & YouTube channel even after you set it to Draft on Online Store, so Google keeps trying to crawl a page that no longer exists.
Google re-checks landing pages periodically. Per Google's own guidance, affected items usually clear from Diagnostics within 24 to 72 hours once the page loads correctly again.
No. Feed Doctor cannot edit your theme, hosting, or robots.txt. It can remove the product from the Google channel so it stops collecting disapprovals while you fix the page, and it will flag the same product again on a later scan if it is still broken.
Source: Google Merchant Center Help: How to fix a missing product page · Google Merchant Center Help: Unable to check product pages