I have had this issue on my MK6 and my MK7.
When I had my MK6, it started around 35,000 miles or so and it would happen when I gave it a little too much in 5th or 6th (sometimes 4th.)
I figured it was my clutch that was slipping so I started looking at options.
I babied it for a while while I tried to decide what I wanted to do until one day, it just stopped. The car was totaled not too long after that so I just forgot about it totally.
Fast forward to about 6 months ago, my MK7 had almost identical mileage (around 35K) and sure as shit, the same thing started to happen!
Most of my driving is highway, so there are times when I give it a little without downshifting, so while being at about 1/2 throttle or more in 5th or 6th going about 60mph, it would feel like the clutch was "slipping"
I remembered back to my MK6 days so I figured once again, I would just baby it for a couple of months and see if it will do away like it did before.
And it did.
As of a couple of weeks ago the car is totally fine.
No more "slipping" under more than 1/2 throttle, no matter gear or RPM.
I still take care though...I don't go more than 1/2 throttle unless I'. getting into the 3K RPM range.
I guess I'll see if this is something that will last...