Not sure if this is exclusive to UHD. I rewatched my blu-ray of Malignant last Friday and had a freeze-up around the 30-minute mark that I don't recall being an issue on my first viewing back last March.
Of course this was right during a particularly tense/surprising moment in the film...
The Classic Monsters Vol. 1 UHD set I just received from Universal is the same. I pulled out Dracula and it had some light smudges and scuffs that I cleaned off. It seemed to play OK. I didn't bother to examine or clean Frankenstein, but that also seemed to play OK. I may watch the other two...