Mail.app shows empty Gmail labels, but they're not empty in Gmail This used to work, but at some point it stopped.  I have labels defined in Gmail. In Mail.app they show up as folders on the left side, like:



That image shows the apartments label. The problem is that Mail.app thinks there are 0 message in apartments, but if I go to Gmail I see 27 messages.

The "Show in IMAP" checkbox is checked in Gmail settings.
I had the same issue, under Mailbox there is a Synchronise option. This worked for me on Sierra.