Help for making MAC computer- Securifi router - Xfinity work

My brother has this setup. He is completely without usable computer knowledge/skills. For months he has been trying to resolve an issue with the system. I keep getting dragged into long useless phone calls. Presumably because of their user interface, Securifi does not seem to have a manual. I am not going to try to work through the menus on the phone with him.

When everything is connected and running, he gets download speeds consistent with Blast. Then after some time the speed decreases...

Help for making MAC computer- Securifi router - Xfinity work