Yes, it is.
Struggling all year round, then suddenly there's more money in there can cause a natural human reaction to actually buy the bread and milk, rather than have it run out - maybe, Heaven forfend, get something a bit nicer like some cheese or buy a larger bag of rice because it works out cheaper that way, but slightly misjudge it or get caught out by post Christmas price rises, travel goes up, the direct debits go up and then there's an extra 2 and a bit weeks to last on top.
Some employers still refuse to report the payment days as being the same when they do the earlier pay run, which means some will lose all of their UC without warning in that time, too.
The other aspect is that people in lower paid, more precarious work tend to have lower numeracy skills - knowing they have so much a week was manageable, but then dividing by six and a half is much harder. Or they just see they've got more in there and struggle to think 'hang on, I've got to not spend any of this for another two weeks' because they're used to spending until it hits zero.
Not everybody adapts well to changes, particularly when they're so infrequent and unpredictable (as in we only got told yesterday that the early payday is Christmas Eve - fine for me, but absolutely not for everybody; other employers might let staff know well in advance, not all do, though.
Let's face it, if you've got somebody who is permanently running out of money, struggles with numeracy and they've got money in their account in the darkest period of year when everything around them is expertly designed to separate people from money through promises to luxury, joy, being worth celebrating, it's not Christmas unless you have x, y or z, it's really, really difficult for them to hear 'no, just carry on being hungry, just because you've got it for a change doesn't mean you're entitled to get some pleasure from it'. They want the heating on because they're cold or the food that tastes good now.