FYI - I didn't get around to trying to rollback the firmware and it looks like it happened again (recording stops at 2h 30m, should have gone 3h, log shows the recording happening the entire 3h). This time I do see "catastrophic failures" in the log for tuner 1, but it's at the recording start time and states no available tuner. But it ended up starting a few minutes later anyway, on tuner 0.
Looking back in time it appears there were quite a few catastrophic failures on tuner 1, but tuner 0 doesn't seem to have those errors. Tuner 1 is the tuner marked as recording the Big Bang Theory show that truncated as well. In this case, tuner 0 ended up eventually handling the 3 hour recording that should have occurred.
I'll try rolling back firmware next week if I can. If that doesn't help, it seems to potentially be a problem with the HD hardware.
Edit: It appears you can't rollback firmware on HDHomeRun devices. Whoever heard of such a thing.... If I knew that, I never would have upgraded the device. I might need to find a new piece of hardware, I can't fathom a company not supporting a rollback to prior versions of firmware. That's crazy.