I recently received this message from an admin:
Hello! You are receiving this message because you have followed a user profile in the past.
Starting on 08/19/2019, we will begin showing some users new followers of their profile. In about 3 months, all users will be able to see all the usernames of their followers, including follows that were done in the past, while the user profile feature was in beta. Please take a moment to check your subscriptions list (where followed users also appear) to ensure that if you follow someone, you are comfortable with them being aware of this.
It's a rather big change and a shame that they are making reddit more and more like the rest of social media.