5 Ghz band not working

I have the xfi router and have set up 2 different network names / passwords so that we can support devices that can only connect to the 2.4ghz band. Haven't had an issue for 18 months. As of last 3 days 5ghz band no longer works. It shows up as a network but when trying to connect it either doesn't connect or if it does (after resetting) it works for about a minute before not working again.

Atfer Comcast merged the network and then somehow made it worse.  I have spearated  them back into 2 networks again worked for a minute and then didn't work after I got off the call with them.