Ok, you have eliminated the Diseqc switch as the cause.
Now it's down to either a signal from the dish, or decryption problems.
Check the signal quality on all transponders you have problems with, are they all sufficient?
You must get to know your receiver so that you know what the minimum quality reading is required to get a decent picture. If there are any transponders with FTA channels on them as well as the other channels you want. Check those, are you getting a stable picture? If so, it's not a signal problem.
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