SP.Folder does not return data related to current site

[SDToews]

#site location of code:
/sites/uat/vanilla

code:

 script.onload = function () {
       sprLib.folder("SiteAssets").info().then(objSiteInfo => console.log(objSiteInfo));
       }

results:

Created: "2018-09-05T16:25:54"
FolderCount: 9
HasSubdirs: true
HasUniqueRoleAssignments: false
Hidden: false
ItemCount: 13
ListGUID: "{CB79ACA3-9E86-4C55-8DCE-88E6CD0E14ED}"
Modified: "2019-03-19T22:02:33"
Name: "SiteAssets"
ServerRelativeUrl: "/sites/UAT/SiteAssets"
TotalSize: 4812042

alternate code:

script.onload = function () {
    sprLib.folder("/sites/uat/vanilla/SiteAssets").info().then(objSiteInfo => console.log(objSiteInfo));
    }

alternate results:

Uncaught (in promise) (404) List does not exist.

The page you selected contains a list that does not exist. It may have been deleted by another user.

URL used: ../_api/web/Lists(guid'5519F739-A6AB-4D49-ABF1-EC6348B314AD')/rootFolder/Folders?$select=ListItemAllFields/Id&$expand=ListItemAllFields

Notes:

may be related/similar to issue #27
GUID in alternate results is correct for the list requested.