Bloom doesn’t work on Mali-400 devices because they do not support floating point framebuffers. We have to emulate floating point for such low-end devices, but our emulation method does not support bloom.
It should work on all modern devices with recent firmware.
As stated above, we don’t support bloom on Mali-400 because the device doesn’t support floating point framebuffers. We need floating point framebuffers (or an emulation method) for the physically-based rendering calculations UE4 performs, and the Mali-400 GPU doesn’t have the features we require.