The most common and most likely answer to this crossword clue is the 13 letter word DYSFUNCTIONAL
I've seen this crossword clue in The Daily Telegraph
D
Y
S
F
U
N
C
T
I
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Buddy explains!

The straight part
We know that "Not working" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not working = dysfunctional.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 DYSFUNCTIONAL mean?
DYSFUNCTIONAL adjective- Not performing its proper or intended function.
- Functioning incorrectly or abnormally; especially, designating of a business, family or social group with harmful, aberrant, strange or abnormal behavior.