Spatial dynamic range can definitely be an issue. Blender uses single precision floating point numbers, so depending on your scene scale there are a limited number of places in a given linear dimension where you can place verticies.
Some more on this at: Cycles sun cast shadow position is WRONG!
Adaptive subdivision is significantly improved in 2.80, but it’s also rather buggy at the moment if you try to use it in a rendered mode 3dview (likely to crash or go into a loop allocating memory when switching view modes or changing subdiv parameters). Seems to work fine for F12 renders.