How fix MacOS Mail so Gmail labels appear?

I recently bought a new MacBook Pro, and set up Mac Mail with my Gmail accounts. At first, when the mail was being imported, the labels for my emails listed in the list preview section of the Inbox / message browser appeared. Then, Mac ran an update for 10.15 (Catalina), and all of the labels for my emails listed in the list preview section of the Inbox / message browser ***disappeared***. I've ensured that the 'Show in IMAP' checkbox is ticked next to all of the labels I wish to see as folders in Apple Mail. It shows the mailbox but not the labels for the messages listed in the list preview section of the Inbox / message browser. Any ideas on how to fix this? I've contacted Apple support, but they haven't provided any guidance.