The phrase "add further difficulty" is correct and usable in written English.
You can use it when discussing a situation or task that becomes more challenging or complicated.
Example: "The unexpected changes in the project timeline will add further difficulty to our already tight schedule."
Alternatives: "increase the challenge" or "compound the difficulty."
To add further difficulty, many will have a long and difficult journey towards diagnosis and proper management, with multiple attendances at their GP and A&E.
The interactive effects between climate drivers and other anthropogenic factors, such as pollution, habitat destruction and overfishing [ 20, 69, 71] add further difficulty to any interpretation of climate change effects.
And from the engineer's perspective, they write, making robots "sensitive to moral considerations will add further difficulties to the already challenging task of building reliable, efficient and safe systems".
Systematic differences among regions in the genetic make-up that regulates metabolism of xenobiotics and reproductive functioning add further difficulties to the interpretation of heterogeneous associations.
The fact that one or more steps of the carcinogenic process may occur as distant in time as in previous generations adds further difficulty to correctly assessing risk [ 3].
The emergence of peta-scale systems and the upcoming manycore era brings nevertheless new challenges to computing systems and architectures, adding further difficulties and requirements on the development of the corresponding simulators.
Cryotherapy adds further difficulties to the measurement procedure, for example, a limited data acquisition time after the cold application.
Also, some sulfur compounds can be oxidized abiotically adding further difficulties in resolving enzymatic steps from chemical changes.
In addition, the reagents needed for microscopic examination of malaria parasite were not readily available adding further difficulties [ 27].
The approaches based on mixtures of distributions, data components or model averaging seem to add further flexibility in acknowledging difficulties in explicitly modelling the skewness in the data.
These properties of the systems cause the difficulties and add further complexity to the design.
