I contacted DGS and received the following answer about new tuners:
"The tuner is ours, that's correct one. Not clone.
We have two kinds of DVB-S2 tuner solution, earlier one is CX24116, and
later one is STV0903. right now, we are supplying STV0903 only.
Actually, our boxes can not be make clone indeed."
and regarding to picture freezes/cracking on HD chanmels :
"Extract the tuner module from receiver, and then re-insert into the
socket with tightly of cause , you have to unplug AC power cord before
open top cover.
I think the problem caused by miss contacted with tuner module and the
socket of main board."