I have been without issue when developing for the past three months until the most recent steamvr update now it will no longer detect unity, I have uninstalled and reinstalled directx11, unity 5.6, and steamvr itself and it still will not connect to unity any help is massively appreciated. Thanks!
Just a shot in the dark, I was having this same issue earlier today and ended up doing an Assets>Reimport All. That seemed to fix it for me.
I just found the Issue!! It seems as SteamVR does not work with OpenGL core :(!. Changing to DirectX helped. For non windows systems, maybe changing to VUlkan does the thing.