iPhone not connecting to Apple TV via Control Center Remote App

Problem: User that recently left family sharing to get their own iCloud/Apple Music subscriptions is no longer able to control Apple TV via iPhone. Leaving family sharing was the only change to the account yet when selecting an Apple TV in the remote app in Control Center, it would show a spinning circle for a few seconds like the app is trying to connect but then the circle disappears without a connection being made.

Solution: When the user left family sharing, HomeKit was turned off in iCloud settings in said user's iCloud settings as iCloud account was changed to a different (user's) e-mail. Turning HomeKit back on under Settings > Apple ID fixed the problem.