In my therapist training courses we were taught that boredom in session = lack of depth/progress/not getting to root of the issue. On one hand you can say its natural to get bored with a therapist over time, but that could be due to them using same interventions over and over again. Or the therapist getting bored of the client saying the same stuff over again refusing to seek different perspectives.

Not saying this is always true but it makes a lot of sense!