Where is the loophole in my code

[Mekire]

Not positive where the error is in your current (likely some index issue) but if you simplify it a bit it works fine.  Note however it is a O(n^2) solution.

class Solution(object):
    def moveZeroes(self, nums):
        i = 0
        moved = 0
        zero_count = nums.count(0)
        while moved < zero_count:
            if nums[i] == 0:
               nums.pop(i)
               nums.append(0)
               moved += 1
               continue
            i += 1
        return nums

I prefer this, though I almost guarantee your teacher will hate it:  

nums.sort(key=lambda x: x == 0)

Why work harder when you can work smarter?