I noticed looking at the postgis_pointcloud scripts that the functions schema qualify both the postgis calls and the pointcloud calls. This will only work if postgis, pointcloud, and postgis_pointcloud are all installed in the same schema.
We had similar issue with postgis_sfcgal and postgis_raster in postgis and put in logic to require that they be installed in same schema as postgis. I need to double-check that though.