It sounds like the clutch friction surfaces are glazed, or that the clutch is heading towards knackered - not sure if that car with that particular engine has a DMF or not.

If it is the clutch, it's intermittent because sometimes, the bearing surfaces 'catch' and engage better than others.

You can certainly roast it a bit to "resurface" the friction plate.

I am very easy on clutches in normal use, I have never had to replace one despite having had a few high mileage cars that probably had worn linings when I got them. But I have suffered what was probably glazing - manifested not as judder but as slip.

It happened on a Honda CRV. I parked up with the handbrake on, set the rpm at 3000 or so, selected a high gear, let the clutch in and allowed it to slip for 5 seconds or so, a couple of times. It cured it, and the clutch was still OK 50,000 miles later, though I had to repeat the treatment once in between.

I can't be certain that it was glazing rather than contamination as I never inspected the plate, but I am of the opinion that glazing was the problem.