Observed behavior (please include a screenshot if possible)

When using the docker quickstart (which is amazing, by the way) The map is simply gray, without any map background. Stop locations are visible but there's nothing behind them. This is an issue even with a mapbox key set in the configuration. Looking at the network tab, I'm seeing requests being made to http://localhost:9966/feed/40a70eaf-9bc1-402b-9867-604a479d12b5/optional-map-tile-url when I move the map around, which doesn't seem to be normal.

Expected behavior

Map should have background

Steps to reproduce the problem

1. Download from commit 6fc72d2148e8dda005aae9c2b26ba911e4197506
2. In the appropriate location (/configurations/default/env.yml), insert your mapbox API key.
3. Run docker-compose up as suggested in README.

Any special notes on configuration used

Nothing special other than changing my mapbox key in /configurations/default/env.yml

Version of datatools-ui and datatools-server if applicable (exact commit hash or branch name)

Commit 6fc72d2148e8dda005aae9c2b26ba911e4197506