Don't know if this is the right answer but I too every so often experience the problems you are encountering.
To solve the problem I just make sure the aerial going into the back of my PVR (Humax 9300-T) is fully pushed in and that the scart leads are all fully pushed in.
If that doesn't work turn off PVR and then back on again and it works.
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Hopefully the above answers your question but just to add I have two video senders in my house too and when I encounter the same problem with them I ensure the scarts are all fully pushed into the back of the additional television sets too.