You might receive notifications (e.g. following, favoriting) which don’t appear genuine. 

First of all: Don’t jump to conclusions! If you check out if someone actually still follows you, you might not see your name in their following list because it is cut off after 500 entries. 

But it might indeed be possible that activities like following and favoriting are just performed to get your attention and then reversed again instantly. These activities might come from either the users itself or bots acting on behalf of those users. Smule is counteracting such practices by setting limits on following, liking and so on. But this can only limit the impact, not remove such practices entirely. 

It’s best just to ignore these notifications. You don’t need to check out every new account that appears in your activity feed, let alone check out if their activities are genuine. Trying to verify their intentions, blocking them or writing them will only cost your time and not really help to contain such problems, which exist on pretty much any social media platform.