Infant, Toddler & Child Milestones disappear every time I go back into the game

Every time I come back into my game after being out of it for hours, or if I enter CAS and go back in live mode, milestones that were achieved in the last game session or a few sessions before that disappear. This applies to infants, toddlers and children for me.

I don't understand why they keep disappearing. It's frustrating because then I have to achieve them all over again, which makes the game not as fun. Also, sometimes when I try to achieve them again, they do not unlock.