We had problems with desktop computer turning on at midnight each night chap came out twice he was baffled but finally sorted it this week .
Then yesterday got in to find all computer turned off printer router etc and also downstairs fridge not power cut rest stuff on lights etc garage freezers finally realised trip switch turned off in kitchen but why ?..?? Glad we were not away as is fridge freezer in kitchen.
I know very little about all that, but I think you may have a faulty switch or connection somewhere that goes on and and off when it feels like it (maybe when the house cools down after the heating is off at night?) As it was the computer that showed the first symptoms, perhaps it is there. Do you turn off the computer at the mains at night, turn it off at the computer, or leave it on standby? That might be relevant to where the fault is. Did the engineer tell you what he did to fix it?
The trip switch would go if a connection is being potentially dangerous. most likely the fault that tripped it is in the wiring to the fridge and the computer. Get an electrician to look at it - the computer chap was only concerned with the pooter.