#3 Alberto Moreno
Alberto Moreno has had a similar story to Mignolet. The Spaniard was signed to solve a defensive problem and looked like the perfect solution. However, a difficult couple of seasons caused him to be out of favour. He received another chance to prove himself and started off well. He would end up being replaced by a better option.
The 2016 Europa League final looked to be Moreno's last game in a Liverpool shirt, but it wasn't. After a year on the sideline, seeing a midfielder take his left-back spot, he worked hard enough to earn a second chance. 2017-18 started with Moreno at left-back, as he did a pretty good job. He then endured another nightmare game against Sevilla, which prompted Klopp to replace him.
An injury against Spartak Moscow proved to be the end of his tenure as first-choice left-back for Liverpool. Andy Robertson filled that void and has been terrific ever since. He looks to be Liverpool's left-back for many years to come. Moreno, on the other hand, would seek a move away from Liverpool if he wants to play regular football. He, like Mignolet, got a few too many chances and it's time to move on.