There was an issue in earlier versions of Telescope due to which if any TIFF file was uploaded with a clipping path, the asset preview would only have the clipping path. This was the case if the ImageMagick I-Piece was configured for TIFF files as there was an issue with ImageMagick 6.9.0 which contributed to this issue.
This issue was fixed in Telescope Standard 2020.1 and it is recommended to upgrade your Telescope version to this or later to fix this issue. If your Telescope installation has customizations or you're an OnDemand customer, please contact your Account Manager or support for help with upgrading.
Upgraded versions of Telescope handle the thumbnail preview generation for TIFF files differently than earlier versions to generate the exact previews.