The most common and most likely answer to this crossword clue is the 7 letter word VACANCY
I've seen this crossword clue in The Daily Telegraph
V
A
C
A
N
C
Y
Buddy explains!

The straight part
We know that "Lack of sense/position that’s open" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lack of sense/position that’s open = vacancy.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 VACANCY mean?
VACANCY noun- An unoccupied position or job.
- An available room in a hotel; guest house, etc.
- Empty space.
- Lack of intelligence or understanding.
- A defect in a crystal caused by the absence of an atom in a lattice