The MPWP should copy over all files from the SD card to the HDD. It is possible that the AVCHD can’t be played back through My Cloud, but it should still be backed up to the HDD so you don’t need to take your laptop along. Try testing this out by inserting your SD card with SVCHD files on it and let it back them up and then connect the MPWP to a computer and see if those files are now on the internal storage.