I reported this issue to Sky as well as the Sky Hub which kept dropping the service (then auto rebooted). Sky tested the line, found a fault and arranged for an Openreach engineeer to attend. The fault was identified and the line in now ok (fibre to box in the street and copper wires to the house).
Since that visit, some You Tube videos buffer on a daily basis - the video freezes for a minute or so and then restarts at an earlier place in the broadcast - maybe about 15-20 seconds before.
This is intermittant and not happening on one specific type of video or one particular contributor.
Sky previously advised that if the fault persisted that they would look at replacing the Sky-Q box.
