Hi @Katalin Balog
Firstly, please backup all the new section groups that are not synced successfully, as any unsynchronized data may be lost once you close the notebook.
Then close the notebook that includes these new section groups in the OneNote desktop app.
Go to www.onenote.com, open the notebook online > Click “Open in App” to sync the notebook to the desktop app.
Please click on each section tab and wait for it to load. After all of this, try to create a new section group and check for sync issues.
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