The phrase "a problematic one in" is correct and usable in written English.
It can be used to describe a specific issue or challenge within a particular context or situation.
Example: "The study revealed that the methodology used was a problematic one in the field of social sciences."
Alternatives: "a challenging aspect in" or "a contentious issue in".
Republicans won the Illinois Senate race in 2010, but it required a nearly perfect set of circumstances: the Republicans fielded a strong candidate in Representative Mark Steven Kirk, Democrats had a problematic one in State Treasurer Alexi Giannoulias and it was one of the most Republican-leaning years in decades.
Some analysts are always trying to unlock the Da Vinci Code by looking at the demographic subsamples in polls – a noble idea in theory, but a problematic one in practice (indeed, I think it is often counterproductive) because the demographic subsamples in polls are subject to considerably more statistical noise than the top-line results.
Leisure is a particularly problematic one in my view.
It is certainly true that Germany's relationship with Israel is a problematic one, with the Holocaust taught in schools and the issue of historical guilt never far beneath the surface.
It's a simple concept - and a problematic one when applied to public services in poor countries.
It was also not clear which government agency or branch of the military was in charge, meaning a "response to a crisis offshore could be problematic", one cable in August 2008 recorded.
Like Heartbleed, Shellshock is a vulnerability, but a much more problematic one because it exists in the basic command line of the Unix operating system rather than in the software used by some sites.
However, the administration of the survey was seen as time consuming, and hospitals found this problematic; one hospital in particular had difficulty finding staff with time available to run the survey.
It is often said that the right ankle is the problematic one – it cracked in the summer of 2011 and forced him to miss 17 months of football – but the left one has not been without its difficulties, initially, as a result of Wilshere over-compensating to protect the right side.
