I have PiP set to live TV only, and get this issue consistently when changing to a recording.
To reproduce:
- Set PiP to live only
- Start a live feed
- Go out to menu screen (live stays in PiP)
- Select an item from the library to watch
The PiP goes black, no sound, but it at least tries to play the video, as the next time you play the same item, you're asked to confirm start from beginning/resume.