I am trying to figure it out but it's not easy to see a pattern. I have 92 available characters.
First time 65 on 1 hour quest....not sure why the other people didn't do it but i thought we'll maybe they don't have 1 hour quests. But 65 out of 91 (at that time) isn't bad.
Second time is put all people on 4 hour quests, so i did and it sent 48 people. So I clicked send all on 1 hour quest and it sent 19 which is 67 people.
I thought well maybe the ones that didn't do it don't have a 1 or 4 hour quest. Well many of them do. But it wont' let me put anyone else on jobs so maybe there is a limit of 65 or 70 people????
I love the new feature but I don't love not knowing exactly how it works.
I did figure out that after they expire there isn't a clear all button, you still need to search for them and click each individual character.