Issue:
In a plan, I can see a different number of followers in the Followers tab and the Insights tab.
Cause:
The Followers tab within a plan does not show or count users with a private profile.
Resolution:
Use the plan's Insights tab to check how many users are currently following the plan – both private and non-private users.
Additional Note:
You can find more information about profile visibility on Change your Profile Visibility.