For a thumbnail to be recognized, the user must first ensure that while completing the data upload process for Assets that the "Thumbnail" column in the "Download Asset Template" is populated. The column should read with the thumbnail name that will be used in the below mentioned ways of system addition.

Asset Template - Thumbnail Column 

Thumbnails can be added in two ways: 

1- Uploading multiple Thumbnails using the "Upload Thumbnails/ Attachments" button 

Data upload - Asset upload

2- While completing the "Asset Template" date upload process, in the row of imported Asset details, select the "Upload File" button in the grid rows. 

Data upload - Uploaded Asset row

For more information about Data Upload, please reference the following video: