Karok Idle moments

 Karok 2.0 diesel SEL Automatic Sep 2018 4x4.  On six occasions since September on moving off from parked the engine will not increase in revs regardless of what I do with the accelerator or the gear lever, this can make things quite exciting if joining a main road and not being able to speed up.  After three times it went to the Skoda dealership in December  who had it for 2 hours and could not replicate the problem.  Since December it has happened 4 more times. Fortunately as I live in an area with little traffic most of the time it has not yet become a major problem because if I stop and switch off and restart then all is well again,  but it is not something to look forward to on joining a fast moving traffic road.  Advice would be appreciated.  A suggestion has been to change the brake light switch as a faulty one could delay the signal  to the ECU