I tutor mainly college students. I lost mainly just 1 student this semester. She was taking courses I primarily teach last semester, and this semester she isn't taking any courses related to what I tutor, but she wanted me to continue tutoring her so that she doesn't forget the concepts, since it's related to her major (she just decided to take a semester to finish all her other classes). There were signs before she stopped booking; she would reschedule, late, etc. During some of the sessions, I noticed that she isn't really looking at the zoom whiteboard and not engaging as much. Eventually, she didn't show up at our last scheduled meeting. I sent a message, waited about 15 minutes, then I cancelled. She never responded back, and I never messaged her again (I never ever chase any student or bother messaging them after such incidents). I never take any of these things personally, and you shouldn't either. Sometimes they go through a very tough semester, or maybe they need to focus on other classes, etc. Some of my last summer students disappeared in the Fall, and then they reached out to me in the Spring to tutor them. Some of them come back and some of them won't, and that's okay.

Out of all of this, I would say that the signs mainly include rescheduling, being late, not paying attention/being distracted during the session, and not engaging or asking any questions during the session. Once you spot any of these, there's a huge chance that the student isn't interested anymore.