I have a SB6121 and had 4 channel bonding on the downstream which worked flawlessly and I was pulling over 40 MBit's down.
I move 1 or 2 miles away, barely even 5 minutes away, and have no bonding at all and am only pulling 24 MBit's or so.
I bought this modem because of the bonding and without bonding, the modem is useless to me and I wasted over $100.
I'm at a total loss... I've called support multiple times and no one can seem to figure out why I am not bonding on the downstream. The only "decent" answer I got was that there are too many people on the node I am now on.