After you file

Sorry, I don't follow you.  Where is that screen shot from?  That's not how it shows on the first page of the 1040 .  And if that is from your return it looks wrong. 

But the IRS letter for son does say he didn't check the box indicating someone can claim  you.  Maybe it got changed before you filed his return, or it was wrong when you filed his and got changed right later.  I would go ahead and amend his return to make sure that b ox is checked or call the IRS.  

Here's a 2023 screenshot showing where to check......