"unrelenting issue" is grammatically correct and can be used in written English.
Example: The unrelenting issue of income inequality has caused much debate and controversy in recent years.
The new kids who have populated the show during its last two seasons are also well-served by the series finale, especially Vince Michael B. Jordann), the quarterback who has had to overcome unrelenting family issues while trying to better himself, and nice-guy Luke (Matt Lauria), who has had family problems of his own.
The subject matter, then, is unrelenting.
The issues, though, remain intractable and unrelenting.
Similarly, a report issued by Unicef on Tuesday said that unrelenting violence, sweeping population displacement and damage to infrastructure and essential services caused by the Syrian conflict risk leaving an entire generation of children scarred for life.
That raises the issue of whether the jurist buckled under pressure so unrelenting it almost got him barred from his grandson's bar mitzvah in South Africa.
"Over the last two years we have been unrelenting in our efforts to try and discover the truth about how the 'selection' issue occurred.
Even those who do well, have underlying issues, tolerable when all else is steady, but which rear their ugly heads under the strain of unrelenting stress.
The pace was unrelenting.
