I have the same problem with using firmware vix 2.3 when I tune in a new satellite and I found this work around to get it working.
Hope it works for you.
Do a manual tune but select just one transponder against the satellite you want to tune in.
This should find the channels connected to that transponder.
Now do the manual tune for the whole satellite.
After a few seconds it should start to scan the satellite as expected.
This seems to be a big in the latest firmware for the Vu+ Duo.
