In the process of dealing with T324801 @colewhite rolled the train back from group2 to group1. The scap portion of that operation took 22 minutes. Analysis of the logs indicates that logic in the mediawiki container image build process determined that the change to wikiversions.json looked like a start-of-week train situation, so it did a full image build instead of an incremental one.
From scap-image-build-and-push-log:
at least one new wiki version is incoming Using multiversion-base:latest as base image