Not sure if this has been reported before but I went to rematch a mare and I'm not finding the stud I wanted. When I'm on the Breeding Center main page, he shows up in the "Remove Stud from Watchlist" part (Highlighted in red. Clearly between Nicholas and Klair de Lune):

But not in the "Match Watchlist Studs" part of the Match Maker. For reference, the list below is my *entire* list, there are no other studs so I couldn't have missed him that way:

Not a bug. That stud is 17 this year which means you won't be able to use LCs in future months. So unfortunately matchmaker will no longer let you make matches with him unless you have a straw.