I remember it started off with Heimdall being able to see Loki again. So Thor went to go get him. When he caught him Loki was mostly complaining about his garden. Turns out Loki had gotten his memory removed from healer in another realm (I think it was vanaheim ?) after he'd escaped from prison. He'd left letters for amnesic!Loki, Thor, Frigga and Odin. He told the new Loki to not turn back. He also sent Thor on a quest... Does this sound familiar to anyone?
EDIT: Never mind I found it myself. The link is: https://www.fanfiction.net/s/9589991/1/The-Memory-Casket