There's some interesting interpretations of the original question.
Louis Vuitton - are they honestly not premium anymore because the monogram and the Damier Ebené are everywhere on Instagram or whatever?
For me premium means two things: the quality of the product, and the quality of the customer experience (sales, aftercare, reliability).
I don't think Louis Vuitton fails on those fronts. I think it fails on the "has it become so commonplace that Mumsnetters believe it's now naff" front, which is always fun for some, but I don't think falls under the remit of the original question.
One answer that does hit the nail on the head is the Range Rover sub-brand of Jaguar Land Rover.
The product is notionally brilliant. A luxury Swiss Army knife of a 4x4, steeped in fifty years of heritage. Was in a class of its own until recently and still is the default for a lot of folk looking for this type of car and experience.
But that experience is tainted for a lot of folk by the build quality and reliability of a car that should be so much better for the price. Electronics glitching constantly, major engine failure on the smaller diesel engines, doors randomly unlatching while on the move, faulty bonnet sensor shutting the whole car down, diesel engines sending it into "limp" mode at 70mph, and then the worst till last.. oil dilution and DPF clogging meaning the cars can fail completely at 10,000 miles or so.
A disgrace at the price they're asking but... they can't stop selling the things because people either don't know about the issues, or they hear about them but want that badge so much they're willing to overlook it