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These are user driven forums, and not official company technical support. There are a couple of Roku employees that moderate the forum, but they are not tech support. They will try to get you in touch with support if necessary.
All electronic devices can fail without warning, regardless of age. I had a defective Roku TV right out of the box, but the replacement has been fine for close to 5 years. I have an ancient 2 XS in a drawer that will still work, but it's performance is so dismal I replaced it years ago. Every other Roku I have has worked fine for years. My old 3600 Stick and Roku 4 are still being used my two of my grandkids. But if any of them failed on me now, I would simply chalk it up to something that failed internally.
My Sharp Roku TV is close to 4 years old, and has been shipped cross-country when I flew home. It has been misbehaving this past week, but I believe it's something in the Roku OS, as I have it in their beta test program and just received a new update. But if it suddenly conked out, it's an electronic device that can fail.
Getting back on the topic of this thread, sudden changes in WiFi signal is usually caused by interference from some other device. Since not every Roku has the same WiFi radio inside, I can understand different models performing differently in the same location. The first thing to try with WiFi issues is simply moving the Roku a few inches in any direction. The radio wavelength at these frequencies is extremely small, so even a minor location change can make a difference. If that doesn't help, try changing the channel used in the wireless access point/router. For the 2.4 GHz band, the best channels to use are 1, 6 or 11. If you're already using one of those, try a different one.