I had the same problem. I deleted both the hub and the timer and readded them and now the timer will not connect to the hub and everytime I call up the app I have to connect to the time wi9th Bluetooth again. This has made the automatic watering feature useless as I have to reconnect to the timer and let the app keep running for it to water on schedule.
I found that I needed to connect with Bluetooth to get accurate battery readings. Sometimes these would be remembered when I reconnected with wifi and sometimes not. If a device was incorrectly showing low battery in wifi, I could control it in Bluetooth, but obviously had to be by it which defeated the remote access.