Loki probably lost to Shanks, but in a way, we aren't used to.

Through the little bits of Shanks we get in terms of him fighting someone, he doesn't fight alone.
He always involves his crew.

Which makes sense. From day 1 of us knowing Shanks, he even says that they're pirates and they dont follow the rules.

So Loki was probably expecting a 1v1, and Shanks just said, "Nah, I dont have to be like that," and then he probably jumped Loki with his crew or with at least Beckman.