Hello Mark,
Are you saying that when a post is sent to the list, it is held for moderation, and when you approve it, it is not delivered?
This is exactly what is happening.
Are there any non-digest members with delivery enabled?
Yes, there is. Some from the imported pck file and some created trough mailman-web
Is the MTA (which MTA) delivering the message to Mailman's REST runner?
I assume it is (postfix) since the message is being held for moderation.
Dec 23 12:35:29 2019 (694) HOLD: lispruebas@mailman3.agro.uba.ar post from brunol@agro.uba.ar held, message-id=<CAOwJ5NX=_bUnfb5ZNqVLFeF3EeOP0GMJW7NeeOWZqVmn5ViyBg@mail.gmail.com>: The message comes from a moderated member
Then the user receives the email notification stating that the post awaits moderator approval. The admin receives notification too.
Dec 23 12:35:47 2019 (701) held message approved, message-id: <CAOwJ5NX=_bUnfb5ZNqVLFeF3EeOP0GMJW7NeeOWZqVmn5ViyBg@mail.gmail.com>
And then nothing. None of the members receives the message