I just bought my 890L in October.  I have a cable modem connected to a switch for wired ethernet throughout the house.  the 890L provides wireless connectivity for primarily iPads but also a new Amazon Echo.  Certain specific devices, including one iPad, my iPhone, and the Echo, have a very difficult time connecting.  Sometimes Speedtest tells me they get 30Mbps, but most of the time they get less than 1Mbps or, frankly, nothing.  Just these 3 devices (all relatively new, so this isn't about old hardware).  I have tried using QoS to "favor" these devices, and when I reboot they will usually work, but then in a day or two they cannot connect again.  I have tried taking all the "cards" out of Qos (since some forums suggest turning off QoS) but that doesn't help either.  I am at my wit's end and about to junk this router and buy a new one.  Any ideas before I waste $300?