Amazon Prime problem - some HD titles only stream in SD
Has anyone else had this problem with Prime? Some of the titles marked HD (examples: Westworld, Rio Bravo, Red Sonja) will not stream in HD. When the buffering screen appears, the bar goes across to 4 dots and the HD symbol never appears. I go to another title (example: The Arrival) and it shows HD. For the titles that work, I can get the HD symbol any number of times. For the titles that don't work, it will fail to show the HD symbol every time. I go to Netflix and every HD title I select streams in HD. I'm using a Roku and I only started having this problem with Prime a few days ago. I know I have sufficient bandwidth, because every speed test I've done recently has shown better than 6Mbps download speed.
When I had a problem like this with Netflix a few months ago, none of the HD titles would stream in HD. I reset the Roku and everything was fine after that. Resetting it has had no effect on the problem with Prime. What is puzzling is that only certain titles are affected. It seems like it remembers that I got a low-bandwidth connection previously and won't connect in HD. I wonder if there is some way to clear the cache so it would be like playing that title for the first time. I tried removing it from the watchlist and re-adding but it made no difference.
Has anyone else had this issue or have any ideas on how to correct it?