My network does the same thing as far as what uses the 2.4 ghz and 5 ghz. But the tech from Rachio had me give each a different name in an effort to fix the issue.
Since separating the two with two different names and putting the Rachio on the 2.4 ghz and my mobile devices on the 5 ghz network it has not gone offline.
The issue does return if I put my phone on the same 2.4 ghz network as the Rachio and then leave me house e a few times.