Dan Lee

This is a problem inherent in random walk-based SSS (the walk hits the internal face, and when tries to evaluate light on it, it's fully in shadow). You can reduce this type of artifacts by increasing SSS limit property (via rendergeometrysettings LOP), which allows the walk to continue from the points in shadow.

Old-fashioned diffusion approximation SSS sidesteps this issue but keep in mind it requires vex-based material and thus won't work under XPU.

Indeed there seems to be a bug currently where mantra's cryptomatte metadata isn't being written out to header when using the new OpenImageIO EXR driver (which is 20.5's default).
I'll log a bug, but in the meanwhile, you can work around this issue by setting the environment variable "HOUDINI_OIIO_EXR" to 0.

Hi. The smeared reflection issue (not relating to the blurry edges due to lack of motion samples that robp already responded to) has been addressed in 20.5.305.