Was having same issue on a laptop quadro A4000, had to roll back from Studio 472.47, a couple to a 460... 463.15, which resolved the problem. Would mean no Optix in Hou19 Karma XPU.

As an aside, the sidefx release notes' HOUDINI_OCL_FEATURE_DISABLE=CL_DEVICE_DEVICE_ENQUEUE_SUPPORT failed to fix the issue (not that I wanted it disabled though, just curious).

Thanks for the fix Grant, this sorted out the same issue here (for 18.5, but we see it in 19 too).

I think for our case the bug may have been associated with this (once?) bug fix (in sidefx change log, for Houdini 18.0.363):

Fixed a bug where OTLs would fail to load on startup with errors like:
"ImportError: No module named sidefx_stroke"

When %HOMEDRIVE%%HOMEPATH% was set to the root of a drive, like Z:\

Maybe it has surfaced again?