When you first find your 'next teacher' on your path, you will be excited because they represent the next teachings that you are ready to be exposed to, and it all seems new and exciting. There is a honeymoon period. It seems to you that this teacher will give you what you're missing.
Over time, you learn stuff, and you start to feel a lack of ease (dis-ease?) and discord and you grow disillusioned and frustrated. The reason is that the lesson here is less obvious. The teacher THEMSELVES are the lesson. Their challenge to you, perhaps the things they've been teaching you, perhaps hold you back in some ways. This is particularly true if the teaching is not teaching the whole truth.
What's required of you is to come to realize how the teacher has limitations and what those limitations are - to become aware enough of the truth that you can discern that this person is not all you thought they were and perhaps there is more truth somewhere else. In other words, you need to receive from the teacher what you came together to share, and then you become awakened enough to realize that its time to move on - that you need a new greater teaching that maybe someone else has to provide.
So the lesson isn't so much, what this teaching is going to transfer to you or tell you about or what tools they give etc. The lesson is, that the teacher themselves are an obstacle and an idol and you need to learn to detach from that and recognize the truth in yourself rather than thinking that it must 'come from' them. You might get to that realization by way of what the teacher is sharing with you, or IN SPITE of it, and especially in spite of it if the teacher is not telling the whole truth. Because if you're making progress, it's because you're waking up and that means you're shining more light and now you can see what you didn't see before.