Tried the beta 4.7.17 and it has the exact same problem. I also tried it on my surface pro where the shaders work flawlessly and pbr looks beautifull.
Interestingly enough when I save a file on my machine and bring it to my surface and open it up I am looking at the same reflectionless, dull shaders. But I can just slap some shiny stuff on top of it and it works, without changing any setting or anything like that.
And now I saved the shiny surface file and opened it on my main machine... and it suddenly works! Not only that, it doesn't just display correctly but it basically cured the problem completely. Now it even works when I open up an entirely unrelated file which wasn't the case before. Soooo I am sure it was some weird software setting that got overwritten by opening a correct file, if that makes sense. Still no idea what it was though, but I am happy now. I suspect the problem is sitting in front of the computer and I would be interested to hear what the problem might have been so I can avoid it in the future.
Thanks for the help!