The most common and most likely answer to this crossword clue is the 6 letter word VAGARY
V
A
G
A
R
Y
More clues leading to the result VAGARY
Buddy explains!

The straight part
We know that "Unexpected change" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unexpected change = vagary.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 VAGARY mean?
VAGARY noun- An erratic, unpredictable occurrence or action.
- An impulsive or illogical desire; a caprice or whim.