'Comprehensive' means including/covering virtually everything.'Comprehensive difficulties' is therefore not a very likely collocation. In another thread, in which your 'comprehensive' was changed to 'comprhension', the reason was that your difficulties were in understanding - in comprehension.
Yes, but this adjective still doesn't work here. "Comprehensible difficulties" are difficulties that can be understood, and not comprehension difficulties.
Yes, but this adjective still doesn't work here. "Comprehensible difficulties" are difficulties that can be understood, and not comprehension difficulties.
No, I wasn't trying to suggest that "comprehensible" should have been used, but the OP thought that the adjective from "comprehension" was "comprehensive". I was simply correcting that assumption.
The title should indeed be "Comprehension Difficulties".