The train blocker[0] mentioned earlier was worked around and train was unblocked. It's now at group1. Watching logs to see if there's any further breakage.
Thank you to Majavah, Urbanecem, and Vlad.shapik (who came up the patch) for unblocking train.
Train will move forward tomorrow to group2, if all goes well.
-- Your humble train toiler
[0] https://phabricator.wikimedia.org/T276316 https://phabricator.wikimedia.org/T274937 https://versions.toolforge.org/