I am a round 3 applicant with an interview invite as well.
Let's just assume that the INSEAD adcom is not in the business of wasting people's time. If that's the case then this year's round 3 will be the same as all of the other years. They invite a certain number of people for interviews and from those they choose a certain percentage, waitlist a certain percentage, etc. They wouldn't schedule interviews with alumni all over the world just to go through the motions and in the end accept only a few. And I don't buy the fact that they are waitlisting a greater percentage or accepting a lower percentage of R3 applicants this year. I think the waitlist and R3 chances of acceptance are exactly the same as they were every year before.
Only the adcom knows the numbers but there's no chance anything's randomly changed this year or that they got trigger happy in the first rounds. Maybe they have been experiencing subpar R3 applicant pools over the past years and now they are accepting fewer in R3 but no chance the percentage changes.
Good luck with your interviews!