Booted up the d64 version six times now. Game seems to run good, except for me at least 2 out of 6 boots (not necessarily restart of game as you lose your life) the game freezes whilst in play. It's brief, only about 2-2.5 seconds duration and not repeated often at all. Game does not crash, both times recovered nicely. However, I would not want it to happen in a theoretical mid-"any tricky jump and then whip" type of situation further into the game.
So I just leave this comment in case it comes up with anyone else. It has not affected my gameplay so far. Nor have there been any crashes or a permanently frozen screen.
system setup: I am using a C64 mini (therefore VICE), PAL setting, and the d64 version.
Have not tried the prg version yet. It doesn't bother me that much.