The problem could be anything at this point.
Arris modems are notorious for not working well with external routers, any Mfr external router as a matter of fact.
Could be that some Arris modems have built in routers in which already can cause connection issues since this introduces double NAT when using external routers. So when you by pass the external router, this problem is not seen when directly connected to the modem with the PC. Could be some odd interaction between the Arris modem and this particular model router or any external router, theres too many to really know what does and doesn't work. Some may work, some may not. Some have been able to get the 835 working using other Mfr ISP modems, and not Arris modems.
I have passed this on to DLink. It's in here hands. If users choose to return the 835 and find something that does work then that is recommended. I would also find a different mfr Modem and test as well. If ISPs support BOYM then I would recommend getting something other than Arris. If your ISP won't support BOYM then, I recommend that users deal with there ISPs and modems or in some cases, if the ISP modem has a built in router already, DO NOT to use an external router, rather get you a DLink DAP model AP device instead. These model APs are just that, wireless APs with out the router functions of external routers. In most cases, these DAP models will work with any modem that have built in routers just fine and where the modem is being the host router and using a external router may not be recommended in this case since this seems to cause Double NAT and connection problems. Usually if the modem can be bridged properly or if the modem has a DMZ option, then maybe using external routers could be used.
Dlink is aware of the problem and it's in there hands. I highly doubt DLinks reputation is on the line here. If your really concerned or bothered how this or any other DLink products work, You need to find something else that does. Again, this may or may not be a DLink issue. Maybe a combination of Arris and DLink at this point. All we can do is wait, or find other solutions. I'm sure DLink is aware of the frustrations that users are feeling. We all hope there is a fix or someone finds the solutions. Until then, make yourselves happier and find something that works. For those that continue to support D-Link and new users with this product, Please contact D-Link support directly. THe more they know and hear about this, the more they will be proactive in getting it resolved and provide everyone with additional help, support, information and a fix.
As far as I'm concerned, the issue lies with Arris, This certain ISP in Canada and DLink. The problem is not seen so far here in the U.S.
This thread is closed until further notice. It will be re-opened if the problem results in further information and or a resolution.
Good Luck.