Client wants to re-download everything after update to 3.0.1


today I updated to the latest client version and - as in the previous updates - first had the old version removed by the installer. But after the update the client removed all folders from the synchronization and after I added them again, it wants to download all data (~300GB) again, although they are present and up to date on my drive. Is there a way to fix this without deleting all data and download everything again?

Thanks for your help!