I have submitted a Bug Report to the iOS Apple Seed Team for iOS 13.4, with no response yet. I will be sure to let you know if I do hear from them.
The controller has not gone Off-Line for over a week now, which is promising. I ran a WiFi Scan, using the iPhone Airport Utility (the hidden WiFi Scan facility); the 2.4GHz band is very poor, RSSI -80, and swamped by stronger (-70 to -75) WiFi at the Rachio 3 install location emanating from WiFi installations in our neighbours homes.
Yesterday (Thursday 20 Feb), I received and installed the WiFi Smart Mesh Booster, re-ran the Airport Utility, and am delighted to note the WiFi Scan now measures RSSI -65 at 2.4GHz (and -73 at 5GHz), and now dominates the neighbours WiFi installations.
I will monitor and get back here again if I see any OffLine or Power Cycle events.