I am having a similar issue with the DIR-826L router that has just started for me. I have two Nokia Lumia Icon phones (929) that just stopped connecting to my wifi network since i updated the firmware to 1.05.
I have the DIR-826L, hardware version A1, firmware 1.05, region NA.
My SSID is a unique name.
Using modes 2.4: N-G-B and 5.0: N-A my phones do not connect.
I just switched the 2.4 modes to N-G and it now seems that everything is connecting.
Any idea if there is some documented incompatibility with the B mode? Hopefully this is a permanent solution and doesn't revert at some point in the near future.