The phrase "a main difficulty when" is correct and usable in written English.
It can be used to introduce a specific challenge or obstacle that occurs in a particular situation or context.
Example: "A main difficulty when implementing new software is ensuring that all team members are adequately trained."
Alternatives: "a primary challenge when" or "a significant issue when".
The main difficulty when building a readable representation is assigning coordinates (in 2D or 3D) to each node of the network.
The main difficulty when using TSM is the assessment of the frequency range where the results are valid.
The meta-stable level related to the 93.3 keV γ-transition represents the main difficulty when using the coincidence method to standardize this radionuclide.
The main difficulty when dealing with this problem is the lack of compactness of the Sobolev embedding theorem.
The main difficulty when applying the periodic unfolding method consists in finding suitable test functions adapted to our elasticity tensor and to the interface term appearing in the variational formulation.
The main difficulty when using the Bosniak classification system is differentiating between category II and III lesions.
However, the main difficulty when reading basic science abstracts related to the omission of basic information such as the formulation of the research objective and clarification of the research design.
Moreover, in the absence of formal training in cultural competence, Belgian health professionals identified the lack of knowledge and skills in cultural competence as one of their main difficulties when caring for migrants [ 54].
For instance, a main difficulty of the WS sequence was detecting a person's leg when the intensity value of the leg was similar to the background intensity value.
A main difficulty of the FT sequence was that a person's pants color was similar to the background region when the person stood against the fountain.
