Thank you for offering a potential solution. I did not need to try it, however.
For two days, the Photo Stream screensaver was failing to show my photos on the Philips Roku TV (even though it was still working on the other TVs). But miraculously, on the third day, it started working again on the Philips Roku TV, like it had always done on the other TVs. I never knew why that happened. I hope it won't happen again.
Thank you for trying to help me.