Why are the lessons not going in the given order and being skipped in the "Intermediate Python" course?

Question

I am taking the Intermediate Python course
(Here is the link - https://www.sololearn.com/learning/1158), and I have noticed that the lessons are being skipped in the course.
The first lesson of the course is "Summary", and second one is introduction. BUT after the first lesson(Summary), the course directly jumped to Exception handling, skipping functional programming and OOP. Because of this issue, I am not able to access some lessons. Why is this happening? Please help me solve this issue....