The most common and most likely answer to this crossword clue is the 6 letter word RANKLE
I've seen this crossword clue in Independent
R
A
N
K
L
E
More clues leading to the result RANKLE
- Out-and-out lies oddly cause resentment
- Bug scampered over wild animal standing up
- Upset as a result of row and left half abandoned
- Class getting the French bug
- Run joint and cause resentment
- Row created by the French to fester
- Cause irritation right on the joint
- Put in order last two appearances of Uncle Fester from years ago
- Offensive Little Englander starts to cause irritation
- Bug scuttled over large beast
Buddy explains!

The straight part
We know that "Fester from years ago" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fester from years ago = rankle.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 RANKLE mean?
RANKLE verb- To cause irritation or deep bitterness.
- To fester.