In versions 3.8 and 4.0, you may encounter issues with missing meshes when importing animation files due to differences in how data is handled between these versions. Specifically, when exporting JSON from a newer version like 4.0 to an older version, you might lose certain data such as Bezier curves because of incompatibilities in how these are stored. Additionally, ensuring that the images path is correctly set after import can resolve issues with missing images. In contrast, version 4.2 has received numerous bug fixes and improvements, which likely accounts for the smoother import experience you observed.