High checkout abandonment rate

In the past few months we saw a slow and steady increase in checkout abandonment rate. The unique visitor count to the /checkout/placeorder page is constant but orders dropped.

Some customers have been reporting they are unable to checkout, where it would give them a message saying we can not ship to their country, even though their country is listed on our shipping methods. At the same time we would receive email notifications from Tindie “Request to ship to Côte d’Ivoire”, even though the customer selected a different country during checkout.

Can anyone look into this?