This is present in the clean copy of the show on ITV Player; I assumed it was an issue at playout's end (not that I'm anywhere near an expert on these kind of things). So a problem with the production itself, I would assume. Didn't look like Dermot was aware of it as he was presenting, though.
Of course, he (and the rest of the production team) had more important things to think about at that point than watching an off-air monitor. Even if he noticed the problem on a monitor where he was he couldn't assume it was going out like that.