Faulty Wipers, indicators, beam lights and windows

Have an 08 skoda that drives perfectly and has passed NCT, however
whenever I drive continuously for over an hour, the window wipers,
indicators, windows and constant beam stop working (even if they were not
on to begin with). The hazaed lights will work and so will the beam light for
flashing. Mechanic had fitted a new fuse box, that did not solve the problem,
has also attached the car to a computer several times to see if an electrical
fault shows up but nothing shows up, and cannot find any loose wires that
may be the cause. Any one have any idea what the issue could be? Have
take it to 3 mechanics in total and none can find the cause of this problem! Other than this issue the car drive wonderfully!!