Hello!
It could be another reason if you sent the medical within the past two years or if the medical is missing a vaccination for any reason.
Other reasons can be very very simple and easy to manage such as more proof of 1-year residency or something else in your application that could need documenting such as employment or travel or family history. No matter what. I wouldn’t worry about it at all
Let us know what it is when you receive it and most likely it’s a very simple thing they’re asking for! keep us posted and good luck!!