Honestly sleaking I got crazy for two weeks with this issue.
I used to have a Humax IRCI 5400 and it worked perfect, then I thought of upgrading to the DM 7025 and since then all shit happened with looking for channels. Since yesterday I solved the problem, finally.
I have two LNBs, for Astra and Hotbird connected over a Diseqc (1.1) 2-1 switch to my dreambox. Tuner B is connected through tuner A.
First issue I had was that in the assignment of the sattelites I had put Astra as port A and Hotbird on port B. The outcome was that the Dreambox would find around 1700 channels but after zapping would then not be able to tune in, especially when changeing between satellites. Only a reboot would give me a picture again. 7 days later I changed the assignment and I now had 3.300 channels.
This did not change the fact, that then I could watch hotbird perfectly, but Astra was a no-go with high BER values unable to lock. Countless calls to the support hotline and also a change of the box I was going crazy. I had tried all the advanced settings they had told me to try but nothing happened. I had changed the tuners just to make sure it was not the one and finally also bought a new Diseqc switch.
Oddly enough, when I changed the DIseqc, I could then get Astra perfectly but not hotbird, when I put in my old DIseqc for a test same thing happened. Then I was sure it was a configuration issue.
I twiggled around with the settings and I think what did it was the menu for the committed Diswqc Command which for Astra was set then to BB and for Hotbird to AA. I also set higher voltage.
Since then it is working fine with the old Diseqc switch.
Still I am dissappointed that an old 6year old Humax worked perfectly and the €700 box was so sensitive on this issue causing me so much trouble and extra costs.
Hope this helps any of you in your quests...