I have two M1001 both running firmware 3.0.44. One of them stops playing after about 2.5 hours. It still streams - the display still shows time passing, goes on to the next song, etc. Just no sound is produced.

Once this happens, it stays that way until I reboot the Roku. Selecting another source (like internet radio instead of Firefly) does not have any effect. Just the reboot works.

Is this just a defective unit?

It's possibly defective.

Let's try resetting it, and if the problem recurs, please contact support.

Let's try to startup in safe mode by holding down any button on the remote and plugging the unit into ac power. Try doing a factory restore. If that fails, boot into safe mode again, and choose software update. Please connect it to ethernet when trying to reinstall the software from safe mode.