My experience from the 2015 and 2017 tours is that a select few fans manipulated the system to allow themselves prime positions in line without actually having to wait in line, going against previously announced venue rules, which put the majority of fans at a disadvantage. Generally, the venue will set a rule saying that people are not allowed to begin lining up before a set time.
What then happens is that a select few fans decide that this rule doesn't apply to them, and start their own line, often not at the actual venue. Then, they show up at the time the venue says the line is allowed to begin, and demand that they be counted ahead of everyone who actually showed up at the time the venue said people were supposed to show up. These people even got violent at the Boston/Foxboro show in 2017. They had been told by the venue that they couldn't line up the night before and that their list wouldn't be honored. They had to be physically removed from the property. And yet, they decided that the line would begin at a Dunkin Donuts and that they deserved to be ahead of everyone who did honor the venue rules, and created a scene in an attempt to get things their way.
These select few people will also start a list, and claim that because their name is written there, that they're actually ahead of you in line. Now, I have absolutely no trouble with the idea of writing down the order that people arrive in, and allowing people to leave the line temporarily to use a restroom or to pick up a sandwich to bring back to the line. I think that's just the decent thing to do. But the "list people" will show up at the venue the night before, put their name on a list, and then go home. Then, they'll come back in the morning, and say that since they were there for five minutes the night before, that they deserve to be in front of everyone who actually did wait overnight.
I sincerely hope that U2's management will do something to curb this behavior in 2018. I have to say, the behavior of those select few fans in 2015 and 2017 really took away a lot of joy from something that had previously brought me so much happiness for so many different tours over so many years.
I think the Bruce Springsteen "lottery" method is a great way to combat this. You show up between 2pm and 5pm to get a numbered wristband. At 5pm, a random drawing is held, and the number selected is where the line will begin. So, if 300 wristbands end up being given out, and #50 is drawn, then the person who has #50 becomes the head of the line and the line goes from #50-300, and then #1 goes in after #300, and then everyone who shows up after the wristband drawing goes after them. It puts control of the situation in the hands of venue and band security, where it belongs, and it keeps things much more orderly. Everyone who shows up early enough to get a wristband gets in ahead of those who don't, but it also keeps people from waiting overnight as it doesn't get you any advantage.
The overnight queues tend to favor wealthier fans who travel from city to city and book a hotel in walking distance from the venue, while putting local fans who have to drive to the venue or have to work at a disadvantage.