if your workflow stopped during the GGAU_optimize_structure_(2x) step, it usually means that the structure (.cif or POSCAR) provided was unable to converge to a minimum energy structure. For such cases, I have found that resubmitting the structure after changing the lattice parameter, i.e. increasing the lattice parameter on one direction so that the muffin-tin radius of two ions don't overlap, or other similar corrections, will most probably solve the problem.
However, if your structure is a very large supercell, I think the runtime exceeds a certain (default) computational wall-time after which your job will be defused by the workflow manager. [I am not completely sure of how this works, but if you check the fireworks workflow outputs, these details can be seen as to why your submission was fizzled].
Similarly, these workflows with WF-IDs 1566099, 1566104, 1566120, 1566137 have fizzled after the optimization step. I have tried re-submission with several such work around, however it fizzled again. I have not found a way to solve for such cases, otherwise changing the lattice parameter and ion coordinates usually work, because you are essentially reducing the energy (arising from strain, ion repulsion-interactions, etc.) of your structure.
Perhaps other super users know how to deal with such cases. ( @dwinston )