Can't save level that has landscape layer material when moving level asset

Can't save level that has landscape layer material when moving level asset.

It look like regression,because it can save level asset in 4.19.

This issue occur also that moving "Landsacape" level asset with "ContentExample" projecat.

1. Open Stylized Rendering sample project
2. Move asset "Stylized_Kingdom" to another folder by drag and drop.

At that time, displayed "can't save .umap" message. (attached file)

If it hide the dialog and restart the editor, the .umap file is lost.