I have the same problem: the bulbs/fuses/etc. all work, but various branches will not light. I think it's wiring.
Since I like the tree, and it is hinged, I am considering removing the attached lights, attaching new LED lights (separate strand for each section) which will plug together when all sections are attached.
I would never consider doing what I heard someone else did: which is to go out and buy a new identical tree, keep the receipt, and return the old defective tree in it's place. You'd definitely get lumps of coal in your stocking.