I had the same problem with my A4. The Peakmeter of input 1 is flashing but in Ableton A4 Vst at ext. in 1 no input.
I think it is a bug or so.
Now I connect my external directly to the audio interface not to A4.
Overbridge isnt stable enough to work without frustrating (Ableton 9 Win 10 AMD FX)