Memo.cash always use the UTXO with highest value in a account.
If I were @Uther, I'll withdraw 20,000,000 sats and redeposit (2,000,000 sats * 10) back to memo account.
I sent my self some more bch and then it started working the next block I think.
because memo.cash will always create txs w/ that UTXO and its children UTXOs. In current version of Bitcoin Cash protocol, the ancestor limitation is 50.