My experience with the Roku network speed test is that it's always lower than it tests on other devices. That said, I've never seen it read zero speed.
From the sound of it, my would guess that you've suddenly encountered some serious WiFi interference. Someone nearby has added a new access point that's using the same channel as yours, or some other sort of radio interference. At the frequencies that WiFi uses, sometimes moving a device or the router a matter of inches can make a difference. I would also suggest changing the channel your router uses as a test. Most routers are set to Auto select for channel assignment, and they may or may not change the channel dynamically if something nearby starts interfering. Find out what channel you're using now (the Roku network info page will show it). If it's near the middle (say channel 6) switch it to one end or the other. If you're already at one end, try the other or the middle. There are free apps you can install on a computer that can scan for other access points and show what channel they are using, and help you choose a channel with less odds of interference.
Dan
Roku Community Streaming Expert
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