With items that have decimal sizes (such as half sizes with shoes), the app is sorting the numbers with whole numbers first and then decimal numbers. So instead of 6, 6.5, 7, 7.5, the app is listing the sizes whole first (6, 7, 8, 9) and then decimal sizes (6.5, 7.5, 8.5, 9.5)

The sizes are sorted correctly on Shopify and even in CS but on the app the decimals are sorted after the whole numbers.