Array.h seems to make <array> header declarations disappear.
Could you describe what exactly happens? Also, what Eigen version are you using?
Just including Eigen and <array> does not produce any problems on gcc/clang (I don't have MSVC installed to check).
The conflict is in-between the deprecated <Eigen/Array> and <array> if someone add "path/to/eigen3/Eigen" in the list of include directories. This header only contains a #error to help porting from Eigen2, so it is safe to remove it for 3.3 since we plane to remove Eigen2 support anyway.
Eigen/Array has been removed.