DIAGNOSIS This is often a power-saving or IP address conflict issue. The Hub might be losing its stable connection to your router, especially if you have a mesh system or dual-band router with the same network name.
FIX First, try giving your Hub a fixed spot on your network. Log into your router's admin page (usually via a browser). Find the list of connected devices (often called DHCP Client List or similar). Locate your Nest Hub and assign it a static IP address or a DHCP reservation. This stops your router from potentially giving its address away to another device and causing a conflict. Also, in your router's Wi-Fi settings, try setting the 2.4GHz and 5GHz bands to have *different* network names (SSIDs). Then, connect your Nest Hub only to the 2.4GHz network. It's more stable for smart devices over distance.
IF THAT DIDN'T WORK On the Hub itself, go to Settings > Device information and note the MAC address. In your router settings, find a feature called "Wi-Fi MAC Filter" or "Access Control" and make sure the Hub's MAC address is *not* on any block list, and if there's an allow list, add it there.
HEADS UP If you're using a mesh system, sometimes the Hub gets confused hopping between nodes. In your mesh app, try pinning the Hub to connect to the main router node specifically, if that's an option.