After some testing, I've noticed that mobs with a higher than normal followRange attribute are not able to detect players in that range, only follow them once aggression has been triggered. 

Example in 1.17: https://www.youtube.com/watch?v=zJMAR2J1bwg
As you can see, both spawned zombies (spawned with the command /summon zombie ~100 ~ ~ {PersistenceRequired:1b,Attributes:[

{Name:generic.follow_range,Base:200}

]} (which gives them a follow range of 200 and makes them not despawn)) do not become aggressive towards me.

Example in 1.10.2: https://youtu.be/6ssRGocd57Q

In this, you can see that the spawned zombie is aggressive towards me, and it is visible as soon as it is in entity render (this is a little hard to see, but if you look closely his arms are held up and he is moving towards me). This was done with the command /summon Zombie ~100 ~ ~ {Attributes:[

{Name:generic.followRange,Base:200}

],PersistenceRequired:1}. I chose 1.10.2 because I have been working on porting an old minigame I made from 1.10.2 to 1.17.1, and I noticed this discrepancy that breaks the entire concept.

I'm not sure how long this issue has existed for, but it's definitely present in 1.17.1.