It's normal, your sd card is in FAT32, you can't have a file most big of 4GB, here it the mlc in 15 part, put all part in a same folder and open the cmd and type
copy /b mlc.bin.part01 + mlc.bin.part02 + mlc.bin.part03 + mlc.bin.part04 + mlc.bin.part05 + mlc.bin.part06 + mlc.bin.part07 + mlc.bin.part08 + mlc.bin.part09 + mlc.bin.part10 + mlc.bin.part11 + mlc.bin.part12 + mlc.bin.part13 + mlc.bin.part14 + mlc.bin.part15 + mlc.bin.part16 mlc.bin
You will have mlc.bin 29,1 gb, you can delete all part
64gb for a wiiu 32gb or 16gb for a wii u 8gb