I have exactly the same problem with partial recordings. I have an HDHome Run Quattro network tuner.
How does one access the logs to determine what happened with Plex or the HDHomerun.
Others have suggested a cause is a weak signal but If Plex knows it is a partial recording then it knows the full recording length. It should persist with the recording to the extent it can. Better a brief interruption during a full recording than the system just stop recording.
Plex needs to fix this problem as it has been going on for years now logging at past posts without any suggestion of a fix.