I have 2 Roku 3's connected to an HDMI switch with PiP functionality. One acts as a screensaver only when idle using the Media Player, the 2nd Roku is only used as a screensaver using the Media Player. Both stream local content from my NAS so there is absolutely no need to save bandwidth. Today I tested the Bandwidth Saver by leaving one Roku's turned off, the other's turned on. Not only did they both return to the home screen, but they both did it in well under the 4 hours (it was about 2.5 hours). There wasn't even a prompt on the one, it just returned home with no warning.
Roku, please see what can be done to fix this. I've seen a few other posts where other people are having the same issue, and it's very annoying!