What troubleshooting have you tried so far?
You may try to turn off the AP Isolation by going to the modem/router interface via (192.168.1.1) then go to internet connectivity > Mobile Configuration, see screenshot.
Let us know how it goes.
Thank you @BasilDV.
I have hard reset my modem/router and also my chromecast. When I go into the internet connectivity screen within router interface, I actually don't get the second Mobile Configuration tab. All I have is the basic tab and nothing is editable there.