The most common and most likely answer to this crossword clue is the 7 letter word DUBIETY
I've seen this crossword clue in The Times
D
U
B
I
E
T
Y
More clues leading to the result DUBIETY
Buddy explains!

The straight part
We know that "Questionable nature" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case questionable nature = dubiety.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 DUBIETY mean?
DUBIETY noun- Doubtfulness.
- A particular instance of doubt or uncertainty.