The most common and most likely answer to this crossword clue is the 6 letter word INCHED
I've seen this crossword clue in Independent
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N
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Buddy explains!

The straight part
We know that "Made slow progress" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case made slow progress = inched.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 INCHED mean?
INCHED verb- (followed by a preposition) To advance very slowly, or by a small amount (in a particular direction).
- To drive by inches, or small degrees.
- To deal out by inches; to give sparingly.
- (in combination) Being a certain number of inches in length.