Hi mate, I did a post on here as I had exactly the same issue with mine after 1500 miles! They said they had never heard of it happening before (which is hard to believe as it seems common) and they took my gearbox to pieces before finding it was actually the flywheel and clutch. They fixed it under warranty but they did then say that if it happened again it would be down to me to pay for the repairs.
I was actually in my first real race with a golf R and after my second gear change, the clutch didn't return to me and showed me right up in front of a golf guy. From that point on the clutch would struggle to return. I bet there is a lot of Cupra owners out there being charged thousands for this repair when it's clearly a fault in the design. What good is a sporty car if you cant drive it properly now and again for fear of the clutch breaking?