The bug
A natural spawned pillager patrols move on their own speed, but when they spot a player, they will stand still and still look at the player.
However, when you're closer to them, they will start moving normally again.
Linked issues
is duplicated by 3
MC-151910
Vindicators & Pillagers inside an Illager Patrol are not approaching the Player from a certain distance
Resolved
MC-155651
Illagers will stare at you at a distance but not come to you
Resolved
MC-267338
pillagers maintain visual contact, but do not react to the player within the proper detection and attack radius
Resolved
This is the intended behavior of patrols - they watch the player at a distance and then attack if the player gets too close, otherwise they are not aggro'd.