I think you hit it on the head - the Triplane, while apparently a great combat aircraft which oddly I've never flown in WOFF, was indeed a maintenance nightmare and one of the big reasons it was phased out for other models which were easier to produce in numbers, maintain in the field, and performed just as well if not better. Looking at you Camel.
In a combat aircraft assorted damage is all too common. Rough landings, forced landings, accidents, hours in the air, and just everyday wear and tear required these planes to constantly be serviced. Plus the occasional lucky Hun or archie. Doped canvas and wood! Imperfect metallurgy and fit. Constant work needed. This maintenance was not Triplane specific but it had to be serviced regularly like all aircraft.
For an example I have read that to work on the gas tank and fuel system you had to remove the wings. Sounds a bit cumbersome alright.