SB6141 modem dropping speed

Your signal page only shows 6 download bonding channels and for full speed it should be 8 which is the max the SB6141 can do. I'm surprised you got 230 Mb/s at all. See if you have 8 channels when the speed is higher. You might need to contact tech support if the channels are changing from 8 to 6. The Arris SB6190 would be a much better modem with 32 channels if your ISP can use them all.