The last MixColumns of encryption has no corresponding InvMixColumns, and the last InvMixColumns of decryption has no corresponding MixColumns. We will solve this by omitting the MixColumns step from the last encryption round and the InvMixColums step from the last decryption round. With that change, since both encryption and decryption omit of the MixColumns / InvMixColumns step of the last round, their round structure remains the same and decryption is the inverse of encryption.