What
If the background session that watches your published artifacts for comments cannot be started, each affected artifact gets an explicit message telling you automatic replies have stopped and to publish again to re-enable them, instead of the replies stopping silently. The failure is counted as adopt_spawn_failed on artifact_live_subscribe.
Evidence
The background session didn't start, so automatic replies to Artifact comments stopped. Publish the Artifact again to turn them back on.
Strings lifted out of the shipped bundle, so the claim above can be checked against them.