Hi, I finished building 42100 yesterday, and also had some issues connecting to both hubs at the same time. Curiously I had no problems on my iPad, but on my iPhone 7 plus I could only connect to the lower hub (tracks and turntable) and not the upper hub that controls all the other functions.
Ultimately I solved it by installing the Powered Up app 3.0 so I could update the firmware on the second hub.
I then went into the Control+ app, selected 42100, then went into the Settings screen, then selected the "Model Data Reset" option. It is a screen with an arrow that curves tot he left. I selected this option, then closed and reopened the app. After doing this I could finally connect to both hubs on my iPhone.
I agree that there are some teething issues with the app. One thing I don't understand is that when using the One Touch control mode everything moves faster, particularly the bucket opening and closing, compared to the regular driving mode. Is this because the regular driving mode is designed to emulate the movement of the real machine?
I also had some issues getting my bucket to close fully. It now closes with a snap at the end, and takes a while to start opening. I guess it is possible that my bucket piece is a bit bent? I think it is very important to look at how far extended the linear actuators are meant to be when installing them. There are 1:1 diagrams that I didn't pay enough attention to.
Other than that, the model looks fantastic, and the functions are great and move quite quickly. The long linear actuators look really cool, but what I'd love to see is Control+ integrated with an automated use of pneumatics :)
I think 42100 and the Land Rover mark 2019 has a great Technic year, but this is just the start of Control+ so I can't wait to see what second half 2020 brings.