What is the relationship between credits and course hours?
In the European Credit Transfer System (ECTS) one credit point 
equals 25-30 hours of workload and you are supposed to do 30 credits 
per semester or 60 per year.

The number of ECTS credits assigned to a particular class is not 
directly related to the hours in class but to the total workload for 
the class.

For example, the master thesis is worth 30 ECTS in most German 
universities, yet there is 0 class time for it. On the other hand, I 
once took a chemistry lab course with 6 credits => 150-180 hours 
workload of which 120 hours where time spent in the lab, which was ok 
because you can't really do much at home except finishing that day's writeup and taking a look at what is planned for the next day.

In your examples, subtract the class time and you're left with around 
180-240 hours of self study (reviewing the material, doing homework 
assignments) for the first three classes and half that for the last one 
- so the 9 credit classes seem to involve more self study and less time 
in class.

That's perfectly fine as long as the overall workload is between 
25*credits and 30*credits hours.

Since your university is in France, I want to mention that France has 
specified the workload for 1 ETCS credit point to be 29 hours.