The VU+ tuner, at least on my Duo 2, requires more signal quality, than my other receivers, to scan in channels, but once scanned in they will work at a lower quality.
I still think your problem lies with your poor signal quality, and the fact that you can scan in SD channels, at such a low quality, seems to support this, as HD channels are more difficult to scan in, than SD.
You can prove/disprove my theory, by taking your receiver to a friends/relatives house, whose dish provides a better signal quality, and scan in some HD channels, on higher frequencies.
If it then works I would check your cable, for any damage, or signs of water ingress, check the connections, and check your LNB.
Other things you could try is checking your Latitude, and Longitude, are correct, and entered correctly, in your receiver, if using Usals.
Switch to Diseqc 1.2. go into the menu. Setup, System Searching, Positioner Setup, and try using the options to increase your signal quality.
Please post back, after nudging the dish, with any increases, in your signal quality readings, on 19.2E.
Either your dish isn't hitting the correct points, for maximum signal quality, your dish has slipped, so the elevation is slightly off, you have a problem with your LNB/cable, or your dish needs re-aligning, starting with ensuring that your pole is plumb.