Attempting to sign SLP transaction (from a multisig) results in "slp pre-flight check failed: transaction is missing inputs or outputs"

[emergent-reasons]

Report at Ben's request. No expectations on a solution but if you do see some workarounds, it would be great.

Tx hex for multiple recipients

Error after clicking "Sign":

slp pre-flight check failed: transaction is missing inputs or outputs
(node: https://bchd.imaginary.cash/proxy)

Same error if I simplify to a single output and if I switch to a different server.

This wallet has successfully sent single and multiple recipient SLP transactions in the past.

[emergent-reasons]

For what it's worth, it seems that downgrading to 3.6.6 release allows the tx to finish the signing process.