Rendering Multi-Stage GLTF Models Using CZML is Slow Initially

Hi there,

I have a CZML file that spawns 5 models at a specific availability time. Each model is in the glTF JSON format (with textures and buffers embedded as data URIs) and is embedded into the CZML file using a data URI.

When the initial availability time occurs during the playback, there is a very noticeable pause where (I assume) the additional models are being loaded into the scene for the first time. This pause seems to only occur when spawning additional models (other entities like points/paths are instantaneously loaded).

After the initial play through, I can rewind the clock to the beginning availability time and play through the entire CzmlDataSource without any pauses allegedly because the entirety of the file is now loaded.

Is this the expected behavior of the CzmlDataSource? I was expecting the CzmlDataSource.load() method to process/load everything prior to animation.

This is using Cesium version 1.113.0.

Thank You!

Update: I was able to reduce the loading time by using glTF binary format files instead.