Sorry took a while for me to analyze the logs you provided. They do show some successful tuning.
Logs show successful tuning for these channels

An earlier attempt to tune channel 2 failed at 19:00:01 as it took almost a minute to get the stream to start
The failures were the following with some tunes taking too long and getting timed out

Do all these tune ok on the PC ? And are they still failing on the shield ? If they are ok on PC using WinTV but fail on the shield with Plex, can you tell me from the wintv config information what frequencies they get tuned on?