I teach both on-ground and online at graduate and undergraduate levels.
Online, there is no reading of body language (which is a high % of "in person" communication) and no ability for the "verbal" student to ask a question and no way for the instructor to see that "blank" look that signals lack of understanding by a student. And yes, students do attend "live" classes and still play on their cell phones on the sly.
When an online or ground student does all their assignments for the week on the last due date I get the feeling that they are not involved, but just "doing the minimum" to get the degree.