Since your on a Cable ISP system, the PPPoE info can be dis-regarded now that we know of your ISP modem configuration. PPPeE is for DSL ISP services which you don't have.
Regarding your ISP modem configuration:
Your model modem seems to be a VoIP gateway modem. This means it may have a built in router: If the ISP modem has a built in router, it's best to bridge the modem. Having 2 routers on the same line can cause connection problems: Link>
Double NAT and
How NAT Works. To tell if the modem is bridged or not, look at the routers web page, Status/Device Info/Wan Section, if there is a 192.168.0.# address in the WAN IP address field, then the modem is not bridged. If the modem can't be bridged then see if the modem has a DMZ option and input the IP address the router gets from the modem and put that into the modems DMZ.
What does the WAN or Internet IP address have on the 810L under Status/Device Info? ##.##.###.### or 192.168.#.?
Your model modem has been discontinued. I recommend asking the ISP for an upgrade at some point. We recommend ArrisMotorola SB 6141 models if your ISP supports them.
Any other WiFi routers in the area that maybe causing interferences? Link> Use InSSIDer to find out. How many? Use v3, its free.
How far away is the 810L from the ISP modem?