Hi, I have the same issue as the OP.
UHD recording plays on both TV boxes but when I try to play from the TV Go app (build 5.10.9253+12927) I see the same as the OP.
This occurs on TV Go installs on my iPhone (15 pro), an iPad and an Android application.
I raised a support request about this and an engineer was sent out today. They said that their internal system has no record of anyone else having this problem. They suggested that the device may not be capable of playing the UHD content. My phone is a current model iPhone so if mine can’t then no iPhones can. It was also suggested I can use the Sky app to watch the content, which is not possible when not live. Which is the point of having the recording like the OP.
I have resorted to recording both the UHD and HD versions.
So I repeat the OPs question, is it possible for the TV Go app to play recorded UHD shows? If it can, then why is it not working for myself or the OP?
I know that I was only recently upgraded to UHD channels, if that changes anything.
@jameselson, you manage to get this working for yourself?