The most common and most likely answer to this crossword clue is the 7 letter word WRINKLE
I've seen this crossword clue in The Daily Telegraph
W
R
I
N
K
L
E
Buddy explains!
The straight part
We know that "Line/problem" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case line/problem = wrinkle.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does WRINKLE mean?
WRINKLE noun- A small furrow, ridge or crease in an otherwise smooth surface.
- A line or crease in the skin, especially when caused by age or fatigue.
- A fault, imperfection or bug especially in a new system or product; typically, they will need to be ironed out.
- A twist on something existing; a novel difference.
- To make wrinkles in; to cause to have wrinkles.
- To pucker or become uneven or irregular.
- (of skin) To develop irreversibly wrinkles; to age.
- To sneer (at).
- A winkle