What word would best fit a situation described as recurring but not consistently?

The word "sporadic" is best suited for a situation described as recurring but not consistently because it specifically refers to occurrences that happen at irregular intervals. When something is sporadic, it means that while it may happen repeatedly, there is no predictable pattern to its timing or frequency. This aligns perfectly with the description of being recurring yet inconsistent.

In contrast, the other options do not fit the context as effectively. "Mitigate" refers to making something less severe or painful and does not relate to the concept of occurrence. "Imperturbable" describes someone or something that remains calm and undisturbed, which also does not pertain to the idea of recurrence. Lastly, "marginal" suggests something that is of secondary importance or minor significance, which does not capture the notion of reoccurrence. Therefore, "sporadic" stands out as the most appropriate choice for the described situation.