Thanks for taking the time to write. We haven’t encountered many issues with the PBS app on Android TV’s in general but a quick web search seems to point to problems specific to the Nvidia Shield product. My suggestion would be to first make sure your TV is loaded with the latest version of Nvidia/Android software and when any update is complete delete the PBS app, download it again and reinstall it. If that doesn’t do the trick here is a link to the PBS Digital help page: What devices support the PBS Video app? : PBS Help. There is a link to submit a ticket at the bottom of the page. They are much more informed on the apps than the local PBS member stations (such as WNED) are.
I hope this is helpful.