i-frame playlist on appletv

I am using an EVENT style playlist with i-frame playlist specified in the master using #EXT-X-I-FRAME-STREAM-INF. This is being played on safari on my macbook and being airplayed to appletv 4th generation (tvOS 11.4). However, when scrubbing back or forward on the timeline on the appletv, I don't see any thumbnail previews (i-frames). I do see requests for i-frame only playlist and also range requests for the actual i-frames in the segment url's in those playlist. Both the i-frame playlist and the i-frame requests are succesful but I still don't see the thumbnai previews. Am I missing something or this is not supposed to work for scrubbing with EVENT style playlist. The thumbnail previews work when scrubbing, if I convert the same playlist it to a VOD style playlist with #EXT-X-ENDLIST.