The most common and most likely answer to this crossword clue is the 11 letter word INCOHERENCE
I've seen this crossword clue in The Times
I
N
C
O
H
E
R
E
N
C
E
Buddy explains!

The straight part
We know that "Lack of clarity" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lack of clarity = incoherence.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 INCOHERENCE mean?
INCOHERENCE noun- The quality of being incoherent.
- Something incoherent; something that does not make logical sense or is not logically connected.
- Thinking or speech that is so disorganized that it is essentially inapprehensible to others.