This could simply be a temporary server issue— try back after some time has passed, and try again..
I got this error now for about a week.
My bag icon says it has 4 items then when I click it the little drop down menu says I have no items in my bag.
I click the Bag link then it says this error "This could simply be a temporary server issue— try back after some time has passed, and try again.."
I've tried on different devices and get the same error.