FindHDF5 is not setting HDF5_IS_PARALLEL
On Linux (at least), the FindHDF5 module from cmake 3.6.1 does not set the HDF5_IS_PARALLEL variable when the hdf5 compiler wrapper is used to determine the C configuration. This worked fine in cmake 3.5.1.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information