Google nest won't show on Google tv

[Babygirl815]

Google nest cameras wireless can't see live feed on my Google Chromecast TV, only shows a camera with a line through it. Why is this & what do I need to do?

[SmartHomeH-TAGS]

3 of my 5 cameras cannot be seen in my app or on Nest Hubs for the last 2 days.

I've reconnected and unlinked the Camera app from Google, but nothing seems to be working. 

Alexa has had no problems.