Continuous Deployment silently failing with 0.23.1

One of our stacks is configured for continuous deployment which worked fine under 0.20 and 0.21, but after upgrading to 0.23 (and then 0.23.1), continuous deployment seems to have silently stopped working.

I can find no errors in the production.log or sidekiq.log, and jobs seem to be enqueuing normally. Manual deployments all continue to work fine.

If I look at the shipit.stacks table in our database, things look normal - pulling out some things that look related:

lock_reason: NULL
tasks_count: 1241
continuous_deployment: 1
undeployed_commits_count: 1
lock_author_id: NULL
ignore_ci: 0
continuous_delivery_delayed_since: NULL
locked_since: NULL
merge_queue_enabled: 0
last_deployed_at: 2018-06-20 01:47:52

With nothing obviously erroring I'm at a bit of a loss as to figure out why it's stopped working. Any suggestions on what I could check?

Thanks!

No source file or test is named. Start by tracing continuous-deployment handling from the enqueued jobs and compare it with the working manual-deployment path, using production.log, sidekiq.log, and the shipit.stacks fields as clues. Done means identifying why deployment stops silently after 0.23.1 and adding a verified fix or diagnostic.