Video player of ThumbnailTiles unable to parse the from the backend's MDP file

Regarding the live stream Dash Trick Play issue, could anyone know how to access the thumbnailTiles field of videoPlayer? I have already set enableThumbnailTilesDuringLive to true, but the thumbnailTiles in the video player remains invalid.
I'm curious why Roku is unable to parse the thumbnail info from the backend's MDP file (fyi: the MDP file does include thumbnail in AdaptationSet).
Any insights would be greatly appreciated. Thank you!