It's not entirely clear to me what benefit there would be to a research team in covertly cloning a human. You obviously can't publish on it, which is the lifeblood of academic researchers. There's no obvious practical benefit to a for profit corporation, unless you want to, like, sell cloning services to rich people...in which case you have to advertise that you can do it. And it's not super clear why most governments would be interested in it.

It's certainly not impossible (especially for groups in the early stages who want to stay quiet until they have success), and after all it's a big world full of all sorts of people who try all sorts of things. I wouldn't be shocked. But I don't in general see a big motivation for people trying to covertly clone people. And generally speaking, people need motivation to spend a lot of money.