When you summon a zombie with a high follow range (55.0, 100.0, etc) it seems to retain it's vanilla value.

Reproduce:

1. Summon villager

summon villager ~ ~ ~ {NoAI:1b}

2. Summon zombie 75-100 blocks away

summon minecraft:zombie ~ ~1 ~ {ArmorItems:[{},{},{},{id:"minecraft:diamond_helmet",Count:1b}],Attributes:[{Name:generic.followRange,Base:100.0}]}

Notice that zombie does not track villager. It will only start tracking from vanilla distance.

This works fine in 1.13.2