The most common and most likely answer to this crossword clue is the 7 letter word POTTIER
I've seen this crossword clue in The Guardian
P
O
T
T
I
E
R
More clues leading to the result POTTIER
Buddy explains!

The straight part
We know that "less stable" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case less stable = pottier.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 POTTIER mean?
POTTIER adjective- Insane.
- Easy to pot the ball on.