The redis problem was of secondary importance, but added significant complexity to the overall git problem. As you can tell from my in-depth post above, I have resolved the issues.
And yes, we had hooked a distributed redis cluster to our Discourse from the very beginning. It’s not managed though, just on other machines.
A failure in connection to the redis-server had caused the app not to start, thus I couldn’t deactivate the theme components in the GUI.
Applying a new redis configuration required an app rebuild, which couldn’t be done due to failure to fetch from the GitHub repos.