5. Data Structures — Python 2.7.18 documentation (same for v3.7)
list.pop([i])
Remove the item at the given position in the list, and return it. If no index is specified, a.pop() removes and returns the last item in the list. (The square brackets around the i in the method signature denote that the parameter is optional, not that you should type square brackets at that position. You will see this notation frequently in the Python Library Reference.)
list.pop(0) is supposed to remove first element, not the last.
Will have to use list = list[1:] for now.
I have some thoughts about why this happens, but either way, it’s a ridiculous bug to be fixed.