Only folders are sync'd but not their content


I’m trying to migrate from OneDrive to Nextcloud but something is wrong with syncing:

Whenever I copy/move a folder into my NextCloud root folder, the notification icon briefly switches to syncing but quickly goes back to up to date. On the website I can see that the folder has been created but is still empty!

If I touch, rename or somehow modify one of the files inside the folder and exit and load the client app again then all of the folder’s files start being synchronised. But not necessarily all the subfolders.

This is a consistent behaviour which happens whenever I add a new folder. I cannot use and trust Nextcloud until I figure out what’s wrong and solve this problem.

Please advise. Thank you.

Server version: 17.0.0 (self hosted in a Proxmox instance in an Intel NUC)
Client version: Version 2.6.0stable (build 20190927)