Occasionally you may need to reboot your entire system. Consumer equipment sometimes just needs to be "turned off and on again". Maybe you are troubleshooting a problem, or maybe the power went out, and after the power returned things were just not working well. When rebooting your system, it is best practice to do a controlled reboot. That is, reboot your system in an order of device dependency (follow the hierarchal path of how your devices are connected). Also wait for each device to COMPLETELY finish rebooting (and give some extra time to "stabilize). Doing a controlled reboot ensures that device dependencies are up and running and in place so that the next device in the chain connects to everything it needs to and operates correctly. See also the Resetting Hubs article. For example:
Cable Modem - boot the cable modem first and use it's LEDs to make sure it connects to the Internet
Router/Base Station - next reboot the router (typically your Wi-Fi base station) and log into it using your computer to verify it is operating correctly
Satellite Access Points - next reboot any satellite wireless access points and monitor your base station to ensure that each satellite has a good connection
Home Servers (Homebridge, etc) - next reboot any servers you have on your network
HomeKit Bridges (Lutron, Hue, Aqara, Ikea, etc) - power cycle all of your bridges so they are up and running before your devices
HomeKit Hubs (AppleTV's, HomePods) - once the "core" of your home network is up and running, give all of your HomeKit hubs a reboot; After they reboot you might want to verify they are logged into your AppleID and connected to your HomeKit room correctly. Give the hubs time to stabilize before you try adding devices or modifying automations and settings.
Devices - typically I treat the devices as an optional reboot, but if you are having problems with specific devices reboot them after everything else is done
You may want to use a similar reboot procedure when updating firmware on your home network and HomeKit devices.