The phrase "difficult owing to" is correct and usable in written English.
You can use it when you want to indicate that a situation or task is challenging or complicated because of other contributing factors. For example, "The exam was very difficult owing to its length and the amount of material covered."
The precise definition of the sides in those fights is very difficult, owing to variations between countries and time periods.
While there is rarely a cover charge at these Moscow night spots, getting in can be extremely difficult owing to the strict "face control" policies at the door.
Walking is difficult, owing to the wide swath of bumpy plowed-in earth, not to mention the deep trench filled with water and still more barbed wire.
Scientific study of owls is difficult owing to their silent nighttime activity, with the result that the ecology, behaviour, and taxonomy of many species remain poorly understood.
Blinding of participants and researchers tends to be difficult owing to the nature of interventions.
However prodrug design is generally difficult owing to the lack of general versatility.
However, the estimation is difficult owing to rapid changes of the line-of-sight direction of the target body.
Evaluation of the oxygen reduction reaction (ORR) on oxide compounds is difficult owing to the insulating nature of oxides.
However, estimation of pre-eruptive H2O content on arc magmas is difficult owing to degassing from erupting magmas.
Large scale culture of marine dinoflagellate microalgae has proved difficult owing to their extreme sensitivity to hydrodynamic forces in photobioreactors.
For example, when FaceBook, AirBnB, or Uber furnish services in Asia or Latin America, receiving payment is difficult owing to operational differences in each market.
