Try resetting the wifi on the Chromecast then reconnecting;
https://support.google.com/chromecast/answer/7331010?hl=en-GB
A factory reset may even be necessary
Otherwise power off/on the hub or factory reset it. You may need to change the network names for each band to how you want them by logging into the hub.
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I know a bit about Wi-Fi, Telecoms, and TV as I used to do it for a living but I'm not perfect so don't beat me up... If you make things you make mistakes!