The phrase "a related difficulty" is correct and usable in written English.
You can use it when discussing challenges or issues that are connected to a particular topic or situation.
Example: "In addition to the main problem, there is a related difficulty that we must address to find a comprehensive solution."
Alternatives: "an associated challenge" or "a connected issue".
A related difficulty is the limited understanding of character transformations.
A related difficulty applies to any consideration of "hits" or "blockbusters": there's no easy way to make comparisons across decades or across media.
A related difficulty is that open-minded observers will want to know why buffoonish impostors can pose such a threat to the great edifice of science.
A related difficulty is posed by the fact, that due to the sheer mole of candidates, the tables and indices at the outset tend to be bulky, un-manageable, and ultimately uninformative.
A related difficulty is the lack of differentiation between learning and development.
Parsons (1970, reprinted in 1979: 150) points out a related difficulty, the 'WOOD = FURNITURE' problem.
A second related difficulty with spectral estimations is the reliance on a clear signal with high signal-to-noise ratio for quantitative assessment of the perfusion state.
There is a second, related difficulty.
A third and related difficulty is that individuals can self-select into certain neighborhoods, and thus their unobserved individual characteristics could once again be correlated within the same residential area.
The main weaknesses were the uncertainty about true age and the related difficulty of establishing a definitive list of eligible participants.
The coded responses for these participants were as follows: 9.7% indicated a sleep-related difficulty, 2.6% indicated a problem related to drugs or alcohol, 24.8% indicated a physical health problem, 34.5% indicated a lifestyle issue, 24.6% indicated an emotional or other psychological issue, and 3.8% of responses were impossible to code.
