netgear CAX80 error message

I have my own netgear CAX80 router/modem that i purchased and I am using Xfinity internet service.  This netgear unit was recommended by Xfinity.  I am receiving an error message on the netgear admin site that says my cable connection is Poor.  I am being told by Netgear folks my input speed is too fast coming into the Netgear unit.  Some people want me to add a splitter to the incoming line to cut the signal in half.  

This doesn't make sense to me.  Why would Xfinity suggest a router/modem that does not work properly with the incoming cable.  

Appreciate any help or insight.

Thanks.

Brian