It's a 1.3+ bug. Some enemies (even sometimes cops) become hostiles even out of sight from far. So when driving, generally you enter in combat for "only" few seconds. In foot, you can enter in combat and "receive" bullets from very, very far (even get a NCPD bounty in worst cases).
Nothing that you can do, except waiting the next update
Probably some enemies not "very far". You can go see if they are directly hostiles there (Three guy with bikes and melee weapons near the main road). For me, it's generally them who "create" this bug around V's apartment (you can kill them to be "safe" for a while, but they "respawn", so the bug could appear again).
Anyway, all of this "random" red map bugs come from this bug of enemies who appeared in 1.3+