Just based on the siting evident in the photo, I'd say shade has something to do with it. But what exactly the hedging plants are could shed more light. Do you know? (photo is too indistinct).

I think it’s called a box wood.
It was doing really well for a long time. Then with in one year it started to die back. It is half under cover and mostly in the shade, maybe it gets 3hr a day of sun. I do water it, and North Vancouver also provides lots of water.

the cement work looks newish ..... was it done after the plants were there ...

is that a driveway .... could we see a pic with more of the surroundings in it .. many things dont grow well right next to asphalt or cement if that is what it is .... ... it could create water and sun issues .... especially if the roots were disturbed by construction ...

ken

Was the front of the hedge recently sheared?

i didnt see the drip line before.. whats your watering protocol?

The hedge was doing great when we moved in (2019) Then 12 months latter it started to die off. The carport and the hedge have both been there for a long time, so the concrete that you see in the photo isn't a new addition to the hedges environment. I have been watering it over this summer because of the heat and the long period of no rain. But generally, it is so moist here with the rain and cool days that I usually don't water it. Maybe it needs a mulch layer and or fertilizer? this is just a guess.

I've heard about hedges getting bare in the middle and having all their leaves on the outside because of how they are pruned, but if it was fine and all of a sudden started losing leaves only on one side...I don't have a good explanation for that. But I'm not a hedge expert either.

If you get to the point where you'd rather pull them out than look at them, you could try (in the spring) the drastic step of cutting one or a couple back (or all of them) to half size, which would remove all the foliage and (hopefuily) cause them to resprout fresh foliage and fill back in.