The most common and most likely answer to this crossword clue is the 9 letter word AMBIGUOUS
I've seen this crossword clue in The Guardian
A
M
B
I
G
U
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U
S
More clues leading to the result AMBIGUOUS
Buddy explains!

The straight part
We know that "uncertain" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case uncertain = ambiguous.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 AMBIGUOUS mean?
AMBIGUOUS adjective- Open to multiple interpretations.
- Vague and unclear.
- (of persons) Hesitant; uncertain; not taking sides.