If you are using a separate digi box if could be
1. a fault with the digi box
2. the scart lead
3. or the scart lead connections on the tv or the digi box could be faulty.
As you have checked that the scart leads are fully in have you tried removing the leads and replacing just in case its a bad contaction.
Have you tried a different scart lead.
If the tv has two scart connections move the scart lead.