As of now please make sure that "show import dialog" checkbox is checked under Preferences>General tab.
Also make sure the Folder you are trying to Sync only contains Raw files,
We are currently investigating the issue.
I've got the same problem if selecting the main directory. If selecting the individual folders, they import ok without having to 'show import dialog". Version 2015.2.1
I don't import; I copy the files and folders to the directory I want on the hard disk. Then I right click teh directory and tell it to sync. It says it found the new files and folders but when it tries to import them at their current location it ends up telling me "No photos or videos were found to import". Creating new preferences file did nothing. I went back to ver 6.1.1 and all is good again. Something in the import in place process appears to be broken.
Our engineering team is working toward a fix for this issue. Until then, please use this workaround:
Enable the 'Show import dialog before importing' option during folder synchronization, and select subfolders to synchronize from the Subfolders menu in the Import dialog.