Entity model heightReference: clamp to ground issue

There are thousands of entities and I am using clamp to ground for entity model and label. It works fine without terrains. But as soon as I load terrain data, the application hangs. Chrome performance tab showing total time around 70-80% for billboard clamping updates.

Everything was working fine earlier but from last week or so, I am facing this issue. I have tried Cesium version 1.111.0 as well as 1.113.0.

I experience performance issue on sandcastle as well, if I add 5000+ entities.