I agree that picture would go a long way to resolving this. Failing that, I would expect it's a typo since the X key is right next to the Z key on a standard keyboard, and typos are so easy to make with today's shrinking technology.
Given that the letter X was not even available with the Journey series, I would be surprised if it made a return to the equipment used to put serial numbers on polymer notes. There is no logical reason why X can't be used on Canadian notes. It has been nearly two decades since X replacements were phased out, and that was on the Birds series which had a completely different font for prefixes and serial numbers.
