FYI - I am a software architect, and guide or build firmware for IOT devices. Including ones with HomeKit stacks. I also participate in matter and Z-wave standards organizations.
I have a properly tuned WiFi network ( and have a spectrum analyzer that I’ve inspected it with. ). The Rachio doesn’t work correctly for me either. I can tell you that this is the ONLY HomeKit device with which I’ve had problems like this. It’s definitely NOT my network. I have Unifi access points and can get 4-5 bars of WiFi connectivity where it’s located.
I can tell you from design experience that the cheap as crap WiFi radio they probably chose could easily be the issue. The fact that it doesn’t function correctly in a dual 2.4/5 SSID environment is one tip off. And even on a 2.4 only SSID, it connects sporadically at best.
Even with other 2.4 only devices that are as far away, or further away, can connect ( the well made ones have absolutely no issue connecting to a 2.4/5 SSID. — cheap modules usually come with a poor WIFi stack as well, one reason they are cheap ).
I suspect the SI they chose really isn’t all that experienced. An Expressif, right out of the box, can do HomeKit as part of the example code. I’ve had one prototyping a device in less than a day, in the same network environment. This isn’t brain surgery, it just requires some competent engineering.
I also suspect they don’t understand MDNS, as that not being properly configured can cause some symptoms like this. But there is absolutely, 100% no reason it should take 2 friggin years and STILL be broken. I could have build a product from scratch and had it shipping in less time.
I wouldn’t be surprised to hear of a class action suit or something because of this. They should have offered refunds or something by now. They strung me along enough that I lost out on returning my unit, which I can tell you I’d have done in a heartbeat if I thought it was going to be 2 friggin years without a resolution.