intermittent servis washer/dryer

hi..wonder if anyone can help with this one..its a servis w/d model M9612W still under guarantee..its got an intermittent problem (happened 3 times since xmas) where when the customer comes to use the machine it lights up as per normal door locks theres a click then all the display goes dead,,no response to any buttons no lights on..if they switch the mains plug off it seems to reset and work normally again…plug and socket ok checked board connections etc.theres no other problem with the machine..thought it might be something obvious im missing..thanks 😕