I'm no expert, but did find this. Could this be your problem? I'd not dig out the plants until you discover whether it's treatable or will infect new plants, too.

Rhododendron bud blast

That is interesting. I'll have to examine the ones that have this a little more closely. It's odd that there are rhodies that bloom reliably right next to the ones that don't. I suppose they could be resistant to the fungus? Thanks.

Rhododendron bud blast is exactly what it is!! It is a fungal disease that is believed to be spread by rhododendron leaf hoppers. It can appear on any rhodies obtained from any sources. Usually requires a two-pronged approach of an insecticide to curb the leafhoppers and a fungicide to address the bud blast and any lingering fungal spores.

I'd expect something like bud blast rather than cold damage to be involved in the described situation as well. As for the 5 degrees that sounds like USDA 8 to me - look at a recent USDA mapping rather than going by your occasional coldest temperature. Also if you look at the mapping of Sunset Zones for western WA these have tended in the past at least to have their Sunset 4 and 5 line up with what the USDA calls Zone 8 (in western WA).

Picture time. Some buds, some foliage, some nicely blooming. The dead buds were rather soft and easy to pull apart, I don't see any blackening of stems. And the new growth is quite healthy looking . The article said they would be hard, though that's relative. It also seems to be affecting these white rhodies more than others.

I seem to remember having similar problems years ago with rhodies I'd planted...most in full bloom when I bought them (from a variety of sources). I have terrible soil, heavy, clay. They all survived but didn't bloom for years and the buds just never opened and died. Then, years later, one by one, they started setting blossoms. One or two per year at first and now they are FULL of blossoms. Not sure the reasons. I left them in place for exactly the same reason as you, they provided screening from the neighbors. I was sad for no blossoms, but didn't pull them out.

It's possible the same thing might happen if you're patient enough. Or, if you're not, perhaps look at other evergreen flowering shrubs so you don't risk the same fate for new rhodies.

In reading further, if it doesn't seem to be bud blast, some articles seem to think it's frost damage that can occur on one plant but not another, because the damaged plant is an earlier flowering variety. Says you can protect the blossoms with cover or replace with a later flowering variety. Do you still have the tags? That can tell you if, perhaps, it IS an early flowering variety that will always suffer damage from a hard frost at a certain time of year.

https://www.glendoick.com/Rhododendron-Problems

The second one in the preceding pictures might be an early flowering caucasicum hybrid but the third one is 'Scintillation', currently in flower up the street from me.

Yes I added that one to show that some bloom just great.