1.47 RuntimeError: Program failed to link. Link log: Could not pack varying v_logZ (1.46=no error)

I should add, the JSON feed is point position data, loaded as Billboard and Label entities with heightReference : Cesium.HeightReference.CLAMP_TO_GROUND
This page has been running fine since Cesium 1.45, and on 1.46, broke at 1.47