Anytime a professor offers an outside of class time "problem solving" session shortly prior to a test, they are letting you know they failed to teach all of the problem solving skills and especially never related practical knowledge. While I can appreciate the dedication it demonstrates on the part of the professor, they should be doing their jobs and putting it in the classroom to begin with.
Wow, I can't believe how wrong this is --- clearly you misunderstood your role in the classroom as a student. In class, a professor should explain the concepts and techniques, but you shouldn't expect them to teach you step-by-step methods of how to solve every single problem in the subject area --- there isn't enough class time for that.
The most important part of the learning process happens outside of class --- when you work and struggle towards learning on your own by working through the problems. Your professor in class is a guide in your learning journey, but they can't do the learning for you --- you need to put in the effort yourself!
When a professor schedules an extra "problem solving" session, they are letting you know they can't be there to hold your hand through that most important and difficult part of the learning process --- the part where you work and learn on your own --- but they understand that you probably got stuck at some point in that process, and are willing to spend their own valuable time to help you get unstuck.