The Call of Duty Vanguard mini-map is borrowing Modern Warfare's controversial feature where it won't display enemies who aren't using a Perk.
That means if enemies aren't using silencers, for example, they won't show up on the map after firing their weapon.
You'll have to use a new Perk to get this ability back. It's called Radar and does, well... exactly what you'd expect. On the bright side, it means you don't have to rely on killstreaks to make enemies visible.
Call of Duty Vanguard Mini-Map Borrows Modern Warzone's Controversial Feature
There's no other use for Radar as yet aside from taking up a Perk slot and restoring the map's visibility function.
Sledgehammer also said the Radar Perk will feature in the upcoming Vanguard beta.
PlayStation owners get access to the beta first, before it opens up to everyone in a few more weeks.