Reuters:

The chief executive of developer Mobicip, Suren Ramasubbu, told Reuters he was interviewed in November by a U.S. investigator who asked about the company’s interactions with Apple. The app, which has nearly a million users worldwide, allows parents to control what their children see on their iPhones.

Ramasubbu said the Mobicip app was temporarily removed from the iPhone app store last year for a failure to meet requirements imposed by Apple.

And:

Six executives of parental control app companies interviewed by Reuters said they had a comfortable relationship with Apple until mid-2018. That is when Apple introduced its own, similar software giving parents oversight of their children’s phone screen time and searches.

When Reuters reports that a “handful of app developers had been contacted”, I suspect (no inside info here, just intuition) that they are all connected to the parental control space.