there is indeed a momentary black at the end of the timeline is a normal occurrence. on android devices, it becomes more pronounced if the image is high resolution which may take longer to load (even if its already cached) thus seems longer. assuming you have just one timeline, as a workaround, you can extend the duration so that the occurrence becomes less - for example, setting the duration to 60min means the occurrence of black is once every 60mins. the maximum duration is 24hrs.
if you channel has more than 1 item and you wish to repeat playing them, enable the channel's property Repeat to Fit - this tells the player to repeat the content to fill the duration of the timeline.
best regards
-ADMIN