In order for an expired subscriber to be included in the Churned Subscriber category for a particular month, the subscriber would need to both subscribe and expire in that same month.
For example, if February shows '0' - that would be the case because none of the subscribers who signed up (and paid an >$0 charge invoice) in February expired in February.
To double check this, you can download the Subscriptions - Churned export for February 2019 (an example) and look at the activated_at column. This will show you the signup day/month for each subscription that churned. If you're seeing '0' for that month in the Churned Subscriber dashboard, then none of the subscriptions in the export should show an activated_at date in February.
Keep in mind that a customer is considered churned when their only or last subscription has expired. This means that if a subscription subscribed in February and expired in February, BUT there was another active subscription on the account that month, the expired subscription would NOT be included in the Churned Subscriber category because the account was still active due to that 2nd subscription.