My experience is that it is more dependent on the router. I have an old Linksys single band with a very long password--20 characters-- that our son set up when he was taking a college class on network security.
The other router is a Netgear dual band and after lots of hair-pulling, teeth grinding and several communications with the Rachio team, I finally got it to connect. My work-around for that router was to set up a guest network on the 2.4 band. Not very elegant, but it worked.
Setting up Rachio with the Linksys was a piece of cake. Both Rachios are Gen 1. The Netgear broadcasts the SSID, the Linksys does not.