The first thing I would check is to see how the stylus looks under a microscope. I have a hand-held device I've used for this since the 1970s. Cartridges can make a lot of distortion if the stylus isn't right!
The other problem I've seen is the magnet structure can shift if the cartridge is dropped or the like.
The other problem I've seen is the magnet structure can shift if the cartridge is dropped or the like.