https://github.com/discourse/discourse/commit/99dd426b12210c93c728a6a8993b9a78430b3b5e
Can you try a new rebuild now @lmcthjo?
Just be sure that in the app.yml it must be:
## Which Git revision should this container use? (default: tests-passed)
version: stable
if you want to run Discourse stable branch (currently 2.2.x).