They had that there before, just in a different place and that is how the listing number and title appears in the subject.
I just went to your store and clicked it to see if it would glitch and not have that info in the subject, but it was there.
I did notice that you also had your own convo link in your description though which didn't automatically add in that info. So that if they are clicking on that link to send you a convo, that is probably why there is no item number in the listing.