I think bad.trace is very similar in the errors (chan_9 instead of chan_7); the difference is probably that the "bad mail" is not using a detached signature (possibly even encrypted), so mutt cannot find the body without actually decoding the message through gpgsm; the "good mail " is using a detached signature, and the body is the first part of a multi-part message which mutt can decode itself; it still can't verify the signature.

I'm sorry; given the original error message

[-- Error: decryption failed: Invalid value passed to IPC --]

I thought it was the same problem I was having.

Hi, I found a workaround for neomutt (see https://github.com/neomutt/neomutt/pull/662).