I have yet to observe anything problematic in those discs. There are so many places in the chain where artifacts can be introduced to the display that aren't present on the disc. For instance, if you're viewing these on a 4K/UHD monitor, something has to upscale that 1080p signal to 4K. Depending on what equipment you have and how its set up, that conversion could be done by your disc player, by your receiver, by your television or by some unholy combination of those entities. And it's certainly within the realm of possibility that any one of those upscaling devices could be introducing artifacts as it attempts to output a lower resolution signal onto a higher resolution display.