It's probably a setting in your router. Make sure you're not using TKIP or TKIP+AES in your Wifi (or WLAN) security encryption setting. It should be AES. (Some phones have been having a problem with TKIP since 4.4. Whether it's the spec's fault or Android's fault is something I haven't determined, and I'm not spending any more time on it, because buying a Netgear N300 for $35 fixed the problem for me, and my time is worth more than that. Even AES on my new Linksys caused the problem - which is extremely low speeds with TKIP. If AES doesn't fix the problem, and you have a Guest mode and using that fixes it, go out and get a Netgear. Linksys doesn't seem to care enough to even look at what's causing the problem. Tell me definitively what it is in the phone that's causing it and I'll keep buying your routers and complain to Google, but they have my money, so they won't discuss it. They never heard that it's cheaper to keep a customer than to get back one you threw away.)