Document thumbnails can sometimes be missing in the Library page when the document store is on a mapped drive. To prevent this happening document thumbnails can be copied to a folder in the local directory which is cleared when Skyline if restarted.
To copy thumbnails to a local directory:
1.
Log in with Host rights and go to Admin.
2.
In the Portals section click Default Configuration.
3.
Find Library - Cache document thumbnails in the list.
4.
click to set the option as True so that the document thumbnails are copied to the local wwwroot\ThumbnailCache directory.
to set the option as True so that the document thumbnails are copied to the local wwwroot\ThumbnailCache directory.
to save the setting.