Sorry to Flabberghaster for forgetting all the details lol, but I re-discovered our postmill.service unit files. Nothing surprising.

It seems indeed the php worker does launch and try - but fails - to download that image

Not in a place rn to do this, but it seems like the thing to do would be to (1) make a Postmill downstream (2) Update the .ini to have a higher memory limit (3) Build new images from that