They devised a potential method to solve the problem, but due to timing issues it became insert word.
A noun or an adjective (or even a phrase) describing this would work. This word would focus on a good plan that was never performed or was incomplete, and not a plan that was attempted but failed and did horribly.
Issues can refer to budget and timing issues, but one would still want the plan as it should work. Therefore it would be used in a case where it was temporarily changed.