Transfer won’t work when the DT is in Overbridge mode, it has to be in USB MIDI mode (bit annoying, you always have to remeber to switch modes if you want to use Transfer and OB)
As for Overbridge not connecting, make sure you have the latest Digi OS (1.11), and the latest version of Overbridge (here: https://www.elektronauts.com/t/overbridge-2-0-17-public-beta/96832)