The most common and most likely answer to this crossword clue is the 6 letter word WADING
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More clues leading to the result WADING
Buddy explains!

The straight part
We know that "finding progress difficult" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case finding progress difficult = wading.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 WADING mean?
WADING verb- To walk through water or something that impedes progress.
- To progress with difficulty
- To walk through (water or similar impediment); to pass through by wading
- To enter recklessly.
- The act of one who wades.
- Appropriate to wade in.
- Which wades (usually said of birds).