I've gotten a message that my site may be knocked off of Google Merchant Center due to "Inaccurate availability (due to inconsistent availability between the landing page and checkout pages on your website)".
This affects only a small amount of products (only around 0.3% of my 40,000-ish products), so I know it's not an engine issue. After asking Google to recheck the results, they came back with the same error, but with a completely different list of products with no overlap, so I know it's not a problem on the individual product level.
There's no geo-locking on these products, and Google says that the problem exists on US IPs.
Nearly all of the errors look like this:
Value on the landing page - v:out_of_stock
Value in the data feed - v:in_stock
Performing an audit on the products in question shows that none of them have been out of stock for weeks, so the data feed is correct.
None of Google's suggested common issues (geolocking, buy button not working, product can't be shipped to an address, products not available country-wide) seem to apply. The country Google checked this on was a US-based IP.
I'm running out of ideas here, does anyone have any other suggestions?
The answer turned out to be something silly for my site, but I'm posting the answer here just in case this helps someone else.
Google's crawler was setting their country to be Andorra and attempting to check out using the US site. This is obviously not a good representation of the US experience. Google advised us that this was a mistake on their crawler's part, and that we would pass the next audit without any modifications. So if you're here looking for a solution, the absolute best advice I can give you is to find a phone number for Google Merchant Center and give them a call because the error may not be on your end at all.
Update: We passed the audit with no changes made on our part.