I'm pretty sure that's not a bug. That's how it is even on a browser. Now, maybe there's a way for the app to scrape the subscription numbers from each instance and display the sum.

This is an issue with Lemmy in general. They didn't respond to my feature request to recreate subscriber counts I made a couple months ago, sadly

I think it happens when instances are not federated. Even upvotes and comments doesn't show up. On all apps it's the same though.