The past 2 weeks or so when following thralls lag and get left behind and or they don’t assist/attack, I noticed a very persistent pattern…
The Bearer thralls lag the most and more often than not, they are stuck on the map until you have another thrall follow you and the bearer goes home. It seems all other thralls lag for a few minutes and then they finally spawn in and catch up to you, where as the bearer never catches up and is stuck where they are, so if you need a bearer to carry a heavy inventory haul, then you’re pretty much screwed!