The monetization icon is applied automatically (via machine learning technology), so mistakes do happen. You can request a review and someone will take a look + update the monetization status if needed! More info here: https://yt.be/help/NW2d
The automated system scans your video multiple times before it’s live & continues to analyze new info once it’s published – this means the icon may change (esp. in the first few hours after upload). We regularly push system updates to improve accuracy, so hope it improves soon!