Why do product sizes revert to smallest at checkout?

We are having issues with customers selecting sizes on products and then at check out the sizes are reverting to the smallest size available? So they may order a size 30-32 on the order and then when they have checked out , the order that we receive shows size 14-16. Any one else had this issue?

Hello @Lisa103 ,

Issue is in your theme JS.
Please try to revert the customizations you did recently or remove the apps you installed recently.
But if you want to keep the customization, call your developer to debug it because this issue arises when you make customization in your theme code.

Thanks