The problem is that the app has no command to search for the Wi-Fi other than the first time it connects.
Try this:
- Make sure the MTH/HOME switch on the Wi-Fi is is set to MTH
- delete the app
- Download the app but stop before it installs.
- power up your TIU and Wi-Fi
- Connect your phone to the MTH Wi-Fi
- go back and finish installing the app
It should discover your TIU. This will work for all iPhone and IOS releases.
Good luck.