Let's look at the context for the term "problematic" in each of the passages:
Passage A says "while the lack of the definition of the terms "minority," ,"people," and "nation" presents difficulties to numerous minority groups, this lack is particularly problematic for the Roma." The author is saying that the lack of definition causes problems to numerous groups, but especially to Roma.
Passage B says "one legal criterion is [required] that they be citizens of the state in question. The last element can be problematic, given the previous nomadic character of the Roma." The author here is saying that the element presents a challenge/ causes difficulty in establishing that Roma is a minority due to their nomadic lifestyle.
In both instances, the authors use the term to indicate that the concept is problematic in a sense that it makes it more difficult to accomplish something, i.e. apply the definition to/ define Roma because they have no ties to a particular country. The passages are not saying that the lack of definition (passage A) or a citizenship requirement (passage B) are difficult to solve - the author never really considers what the solution could be, he merely points out the challenges/ difficulties in the application of these concepts.
Let me know if this helps and if you have any further questions.
