Model C6250 dropping 2.4 h only

The bandwith 2.4 is constantly dropping below 1mbps. ISP speed is 200. 5G works great.

Tried changing channels, MTU and number of devices connected.   Netgear says it is cable to router/modem. Have changed to new cables and different sections of house. Still drops.  Xfinity says it is router/modem. Any ideas