The biggest cause is rushing the install and not following the instructions. Sounds funny but so many people have done it that it is my first assumption whenever I hear about clutch issues.
The clutch pressure plate bolts that hold the pressure plate to the flywheel need to be cleaned off with brake cleaner and wiped clean, then they need red locktite applied to the threads, and they have to be walked down in a star pattern. Starting with finger/socket tight, then they need to be turned 90 degrees at a time until they are tight, and then finally torqued to spec.
It is very important that the red locktite be used or the bolts can back out causing the pressure plate to warp. Also the pressure plate bolts have to be walked down slowly in a start pattern or it will warp the pressure plate. It takes time to do the whole procedure correctly and it and be frustratingly slow at times. Especially if you don’t keep checking that the clutch disc is aligned correctly so the whole thing has to come apart and then go back together a few times.
Sounds simple enough but I have seen morons mess up installing factory clutches and flywheels. One guy in particular used an impact to fully tighten each pressure plate bolt all the way down at a time. On top of being so stupid he went clockwise tightening the bolts all the way down one at a time. Talk about a major screw up.
At least with the B8 style cars the shop is much less likely to mess up installing the flywheel to the back of the crankshaft like with the older B5/6/7 cars. Those cars required the flywheel to be walked down when being installed too because of the interference fit.
