Directly using the Import dialog is usually better than syncing a folder.
From the Library module, in the Folders panel, are any of the folders marked as missing?
Mac or Windows? What version?
Agree I should have used the Import ...
No folders are marked as missing, and I don't have any photos either that appear as missing. Regardless which folder I try, they all give me the same behaviour. Lightroom is running on OSX El Capitan (10.11.6).
hm... guess nobody is experiencing this..
I am experiencing the same thing. running sierra 10.12. What is stranger is that i tested one folder where I synced it, and it shows up on my catalog. Then immediately I sync it again and the same dialog box appears showing i need to resync the 40 pictures. When I press sync, the dialog box for "new pictures" is empty. I can resync if I click on "new" tab. That is, it is not recognizing already synced photos. Just to be sure, I used the "update folder location" function, and it know exactly where everything it. Would love to see if anybody has an answer to this.