Created an account just to say "thanks" and share that I had the same issue and it has now been resolved.
I, too, had a 5th baby born in 2020 and claimed a $1,100 difference on my line 30 because the baby did not receive stimulus payments #1 or #2. The IRS kept my return for over 3 months, then "corrected" it by removing my credit.
When I called (right when they opened on a Monday morning, waited on hold for about 60 minutes), the representative said the issue was that my newest baby was not counted because she was not listed on the 1040 where there are only 4 lines.
My return, which was completed by software, had checked the little box there that says "I have more than 4 dependents and they are listed on a separate statement". The 5th child did receive the CTC.
At first the representative insisted that I would have to file an amended return and that they were correct to have denied the payment because my child wasn't listed on front of the 1040 page 1. I refused to accept this answer, and kept asking questions like, "Where are you supposed to include the dependents if you have more than 4?" (on a separate statement, which I included) "What does that little box mean?" (look at the separate statement) "How did they receive the CTC if the system didn't receive their info?" (the system did in fact receive the info on the separate statement)
Eventually I was put back on hold, waited 15 minutes (while she presumably consulted with someone), and was then told that yes, I had done everything correct, and yes, I was eligible for that payment. She said it would be sent.
I checked my tax account transcript online and can now see a new, additional $1,100 credit backdated to April 15th.
So it ended well, but (1) be persistent! even if the representative says you don't get the credit or that you need to refile, and (2) this seems related to the 5th or higher child being born in 2020.
But again -- thanks for this thread and all who wrote, it's what gave me encouragement to push for that credit.
