Second tx does not appear after approve tx is confirmed

[john-light]

I am testing Multisender on Rinkeby.

I have created a multisend with 3 recipients, transferring 1 DAI to each.

I am using Frame + Aragon Agent (a smart contract account).

I have passed a proposal in my Aragon organization to confirm the approval tx:

However the Multisender dapp does not ever send the second tx needed to complete the transfer, and it gives me an error message suggesting I contact support:

Any idea what might be going wrong here?