Infant constantly reaching milestone

I had my adult sim practice sitting up with their infant for the first time, and then followed it with tummy time. After the tummy time, my infant got the sitting up milestone which I thought was odd since they had only practiced once and they didn't even get it after practicing it, they got it after tummy time. When I went to check the milestone list, it wasn't there. After this, the infant was in a constant stage of reaching that milestone whenever it was in the playmat (i only ever put it in the playmat or crib pretty much), causing the parents to constantly try to come over to watch the milestone. The baby wouldn't do the animation for the sitting up milestone and I wouldn't get the notification, but it would repeatedly show up in his task bar.