[GRO] Practice Standing With Infant Not Queuing

So I did see this same thing a while ago in my game. I was eventually able to get it to happen by having the parent "practice standing" with the infant outside where there was more space, and by putting a stand alone chair nearby to be sure the infant had something easily accessible to pull themself up on. Once I did that, it worked. They practiced standing and then the infant crawled right over to the chair, pulled themself up and achieved the milestone. So it may be happening if your infant is about to achieve the milestone during their next practice session, but the game doesn't think there is enough space available or a readily available chair to pull up on. Could be worth trying.