I put a seed generated by Zashi into Ian Coleman’s Mnemonic Code Converter ( BIP39 - Mnemonic Code ) and checked out the derived addresses. The transparant address shown in Zashi is only the 4th derived address at m/44’/133’/0’/0/3
To derive a Unified Address from a UIVK we need to choose a diversifier index, which MUST be valid for all of the Viewing Key Types in the UIVK. That is,
A Sapling diversifier index MUST generate a valid diversifier as defined in ZIP 32 section “Sapling diversifier derivation” 18.
A Transparent diversifier index MUST be in the range 00 to 231−1231−1 inclusive.
There are no additional constraints on an Orchard diversifier index.
Your seed didn’t generate valid sapling receivers for indices 0-3.