I have a multi-folder file structure (project files within month folders within year folders).
Importing pictures from the top level folder correctly identifies the number of images to import, the progress bar shows the synchronizing in progress, and once the progress bar flips to "Import files ..." it then comes back with "No photos or videos were found ..."
The import works fine if the synchronization is done on a folder with no sub folders.
Version 5 worked fine.
We are able to reproduce this at our end.
The workaround is to select the option to show the Import dialog before importing.
A number of people have experienced this bug. Please add your vote and description of your issue to this topic in the official Adobe feedback forum: Lightroom CC 2015.2 synchronize folder does not import new images unless show import dialog is active. This will make it more likely Adobe will actually prioritize a fix (even though they've acknowledged the problem, that doesn't mean a fix will necessarily appear in the next release).