Dan Lee

Hi. I might recommend a workaround in shader (eg use rayimport VOP to set IOR of glass to 1.0 after X number of bounces)

That is odd - I'm unable to reproduce it on my end (both vector3 and vector2 primvars can be read with either vector2 and vector3 signature on the geomprop VOP).
Can you please file a bug with an example scene? Thanks.

My gut reaction is that you may have accidentally wired a color/vector3 value into Mtlx Displacement VOP's 'displacement' input, which turns it into vector displacement (and the discontinuity in tangent frame could lead to such artifact). If this is indeed the case you'd have to use Mtlx Separate VOP to split the color into floats, and wire one of the float values in instead.