I often meet the phrase in my reading of news reports, the latest one being 中超重新开赛在即，但仍然一地鸡毛. What does the writer imply?
一地鸡毛 is not an idiom. It is the title of a novel by Liu Zhenyun (1991)
Because the novel deals with the ordinary, mundane lives of ordinary people it was extended, by readers, as a social comment on the triviality of everyday matters of daily life, and later extended to anything messy, like the present state of mainland Chinese league football; much like a football field littered everywhere with chicken feathers. An insult I suppose.
Why chicken feathers?
There is an idiom, “鸡毛蒜皮" (Jī máo suàn pí). It literally translates as “chicken feathers and garlic skin”, to describe anything worthless or unimportant.
For the story behind the idiom -- https://www.echineselearning.com/blog/learn-how-to-use-a-chinese-idiom-of-triviality
There is actually an English legal principle -- "de minimis"
A legal term meaning too small to be meaningful or taken into consideration; immaterial. As a matter of policy, the law does not encourage parties to bring legal actions for technical breaches of rules or agreements where the impact of the breach is negligible.
Seems to get used a lot in connection with the Chinese Football Association! Not sure what that tells us!
I find 3 slightly nuanced meanings for:
Can act as an alternative expression for the triviality of daily life.
It indicates something is mediocre, petty, base, without initiative, hopelessly muddled
Also has an extended meaning of "too bad, vexing, confused, make people fed up, something unwelcome."
There are some agencies vying for candidacy who started a dispute, who even appealed to the Chinese Football Association, it really is a muddle.