How long is “always”? If you have been having trouble, why it this the first time you posted here?
What is the RSSI (signal strength) currently reported by your Rachio? See my post in
What is the path like to your router? For example, are cars in the garage in the path of the signal?
How often does the controller disconnect? Does it recover by itself? If not, does it recover if you simply reboot it (remove power, wait a few seconds, power it back on)?
ISP? Modem make/model? Separate router, if any? Any additional access points, repeaters, etc?