This is an old feather that my bird has dropped. This is from his first molt. The missing bits have gone missing because there were weaker spots in that part of the feather due to either malnutrition or stress as he was growing that feather.
It looks to me like your baby has a few stress bars.
How old is your bird and what kind of diet are they on?
There are a few possibilities.
When a tail feather experiences trauma during a vital growth stage, such as falling during a flight attempt, it can cause disruption in the growth that can cause physical anomalies or coloration changes. The next time the bird molts, this will be absent from those feathers.
As @Shezbug mentioned, though, it can also be other stresses during the growth of the feather. They usually manifest as "stress bars" which is a weaker part of the feather. This can be from emotional or physical trauma (not direct trauma like I stated above) or more likely, from lack of nutrients during that stage of the feather growth.
She/he was hatched in May. She’s eating a combination of seed/pellet mixture and fresh fruits and veggies once or twice a week. I’ve never seen her eat any of the vegetables and I see more pellet in the dish when it’s freshened. Water if filtered.