My first thought was scale insects, but you say that the brown areas are INTO the leaf instead of bumps... That suggests that whatever was munching on the leaves either moved on or laid eggs into the damaged areas. It's tough to positively ID a missing muncher.

I would suggest stripping any damaged leaves, and spraying the plant and any adjacent plant with insecticide soap/ Neem oil for the next couple weeks in the evening.

Friend did strip damaged leaves and is watching this plant and those nearby. So far, it was the only one affected. New growth will tell. And I'll pass on the insecticide soap/Neem oil suggestion. Thank you!