@Madcats - I thought SNAFU was a Wordle solution that many grumbled about in recent months - I don't think it was a Plusword.
From the livechat, one interesting comment from the setter:
“It's not a precise science, but the general aim is that, in common with other Telegraph puzzles such as our Cryptic Crossword, PlusWord generally gets more difficult throughout the working week, and slightly easier again on Saturday and Sunday.
“It's a mix of things that makes a puzzle trickier or easier than the average: whether any answers in the crossword grid are out of the ordinary, the actual PlusWord (words with two or three letters the same are generally more difficult to work out), and the number of shaded cells in the grid. I'd like to think that we get it right most of the time.
“Having said that, it's definitely the case that difficulty is in the eye of the beholder (or, more accurately, in the eye of the solver). It's almost a given that for any particular puzzle, some solvers will say it was harder than usual, while others will say that the same puzzle was less of a challenge! And I think any PlusWord solver will know that struggling on just one particular answer for the crossword grid can ruin what was shaping up to be a good time.”