Can you find which circuit breakers in which panel are feeding these lighting circuits?
I would recommend investing in a circuit tracer and toner/tracer set if you don’t already own one. Especially since this building sounds like it’s going to be "your baby" from now on. They can sometimes make problems like this a lot easier to tackle.
Since we are shooting in the dark anyway, is it possible these lights are hooked up to an autotransformer dimmer or something that could be incorrectly wired and somehow acting like a boost transformer?
If you are sure it’s a 208V supply, even with a bad neutral connection, I can’t see how there can be 255V anywhere in the building without some type of transformer ahead of it. I just noticed that you’re in Canada though and I’m really not at all familiar with the type of materials and wiring practice used there .
