The most common and most likely answer to this crossword clue is the 9 letter word THWARTING
I've seen this crossword clue in The Guardian
T
H
W
A
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T
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Buddy explains!

The straight part
We know that "Frustrating" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case frustrating = thwarting.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 THWARTING mean?
THWARTING verb- To cause to fail; to frustrate, to prevent.
- To place (something) across (another thing); to position crosswise.
- To hinder or obstruct by placing (something) in the way of; to block, to impede, to oppose.
- To move (something) across or counter to; to cross.
- An instance of blocking or obstructing.