Hi,
I try some checkout field editor witch has worked before with other themes, but now with GeneratePress I can hide, place next to each other fields,but NOT to reorder.
that plugin says it is only tested up to WP 4.9 and Woocommerce 2.5. The woo version is worrying as this is really out of date and is more likely to be the problem as significant changes to Woo templates has occurred since then.
This topic here provides the filter for re-ordering woo fields which works with the latest version if that helps: