MB8611 Downstream Bonded Channel Corrected and Uncorrected Errors

Experiencing slow speeds (5-20 Mbps, have an 800 Mbps plan) and network dropouts/resets. Online troubleshooting says all systems indicate they are healthy. This is my second MB8611 modem that this has happened on. First modem Motorolla replaced, now they are telling me to have Xfinity check my home.