Migrated my Gmail accounts to Thunderbird a few weeks back from Outlook 2013. I've noticed that unlike Outlook, I never see a new messages flag for the Spam folder until I click on it. Today I remembered to check & as soon as I selected the Spam folder, a number of messages appeared that weren't previously flagged as new messages. This has the potential for an important, incorrectly message marked as spam not being seen until I remember again to check the folder manually.

I've double checked that the folder is subscribed by unsubscribing, in which case the folder disappears. So why isn't Thunderbird flagging these new messages?