The plants are indoors and no bugs have been spotted, you would think the worms should be easily spotted. Also I forgot to add that it's only occurring on one plant
Do you have a cat? Mine gets me all of the time. (That evil little furball) Other than that it does look like bug damage. Look at the main stem and all along the branches. Especially the underside. They are green and blend in well when resting. Good luck!