SOLVED!
Tests with another receiver confirmed it is not a dish/LNB problem. After juggling with various images I've decided to downgrade the FPGA.
I've installed FPGA 4.2, 4.4 and finally 4.5 which repaired the scanning. I've been lucky to keep this last firmware on my computer as I could not find it anywhere on the web.
Thanks to all who responded for suggestions.