Hello!
I created an account here to post this additional solution that worked for me. I hooked up a brand new 890L this week. It shipped with the 1.03 FW. Using the proper FW upgrade method I loaded the latest 1.07 with the security fix. All seemed to be going really well, except mobile devices were crawling when on WiFi. With the 890L, a Moto Surfboard supporting DOCSIS 3 and my 150MB/s Comcast connection; I was able to pull down almost the full 150mb/s from areas across my house. Mobile devices were hanging on loading web pages no matter what. This occurred on my Nexus 6, my wife's iPhone 5 and a friends iPhone 6.
I quickly found the support FAQ that suggested you turn off IPV6 entirely for a quick workaround fix. That did work, but I was convinced there had to be a way to get IPV6 running and getting mobile devices to play nice. After reading about IPV6 and Comcast's implementation I was able to settle into a working IPV6 setup with no mobile issues on wifi. I can't guarantee this will work for you, but it definitely is for me on Comcast (Pennsylvania).
In the router settings > Internet > IPV6 tab I have the following config:
My Internet Connection Is: Auto Configuration SLAAC/DHCPv6
DNS Type: Obtain a DNS server address automatically
Enable DHCP-PD: Enabled
Enable Automatic IPv6 Address Assignment: Enabled
Enable Automatic DHCP-PD in LAN: Enabled
Autoconfiguration Type: SLAAC+Stateless DHCP
Router Advertisement Lifetime: blank
Hope this helps!