Thanks for the great theme. There’s a UI bug I noticed on checkout page.
When you click “Place Order” button WooCommerce JS should place overlay with spinner over the whole page to indicate payment is processing and preventing you from clicking the button again. This is done with jQuery BlockUI library that they use.
In Leto theme however this overlay does not appear - you can see it on your demo as well.
Can you please suggest what the reason may be so I can fix locally? Would be great if you could apply this fix in future releases as well.