say, incompatible exhaust design that can go wrong.
All turbos are designed with the same type of seal technology yet not all turbos will smoke. You basically raise the chances of the turbo leaking oil into the exhaust and creating notable smoke by reducing backpressure in the exhaust.
Even with a very free-flowing exhaust system, some turbos will smoke and others wont. It all comes down to the tolerances at which a given set of turbos are built to.