The most common and most likely answer to this crossword clue is the 10 letter word SUBHEADING
I've seen this crossword clue in Independent
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Buddy explains!
The straight part
We know that "a secondary issue" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a secondary issue = subheading.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 SUBHEADING mean?
SUBHEADING noun- Any of the headings under which each of the main divisions of a subject may be subdivided
- A heading or caption subordinate to a main headline, heading, or title especially when inserted as a divider between sections (as of a newspaper or periodical article or story or text of a book)