But this isn't Lokis arc, this is Imu's arc. In the Kaido situation, we heard about Kaido and Shanks clashing a decade before Wano, and it's pretty likely Oda just forgot about the plot point, or didn't feel like adressing it. In Elbaf, Shanks stopping Loki was introduced as a plot point and one of the facts we were told about Loki, along with him killing his dad for the legendary devil fruit, killing 100s of guards,being an arsonist etc. If Odas goal was to protect Loki, there would be no reason to even mention it. The reason we didn't see Loki and Shanks in the FB is most likely because the entire FB was really just about hyping up Imu and the Gods Knights and how he killed Rocks/Harald.