Updated our internet service now our Chrome cast devices won’t stay connected

We updated our AT&T router to a higher speed and now our Chrome cast devices won’t connect or stay connected. Plus, our Solar City which is hardwired in won’t stay connected.

I’ve powered down the router, and reset both of the Chrome cast devices to factory settings and sometimes they connect, but usually drop their connection. Now they don’t even show up.

When we had the slower router, all would connect and stay connected. 

Any suggestions?