The most common and most likely answer to this crossword clue is the 3 plus 2 plus 8 letter word SEA OF TROUBLES
I've seen this crossword clue in Financial Times
S
E
A
O
F
T
R
O
U
B
L
E
S
Buddy explains!
The straight part
We know that "Main reason for distress" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case main reason for distress = sea of troubles.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.