Hi Tony, I found out the plugin giving this problem is:
SITEGROUND OPTIMIZER
That plugin was causing the problem with xstore cart – not updating free shipping ; if other people are reading this maybe the info will be helpful.
Anyway, JFYI, I double checked what I said in my previous post, and I confirm that on your demo site the very same problem is present.
Take a look here:
https://webm.red/mqd3