Dear Islam,
Welcome to the forum here.
It seems that I can't reproduce the issue in our environment.
From your description, it seems that the issue only occurs in one notebook in your environment.
If yes and if you haven't tried restarting your iPad, I suggest you give it a try and then do a test again to see the result.
Meanwhile, I suggest you get a Windows computer>open the notebooks in OneNote for the web>check whether the affected notebook is synced fine. If yes, open OneNote 2016 to export and upload the affected notebook as a new notebook. Then you can open OneNote for iPad to see if the issue doesn't happen in the new notebook. If yes, you can just remove the old notebook and use the new notebook to move forward in your environment.
Thanks for your effort and time!
Sincerely,
Cliff | Microsoft Community Moderator