Some users in asia-east1 could not access environment variables at build time

This incident has been resolved.

A slow-rolling update to the build system of Firebase App Hosting broke customers' code from being able to see environment variables defined in YAML files. Though the rollout started Monday October 6, we have not correlated this with any customer reports before 8P PST Thursday October 9. The experiment has been rolled back and most customers were never on the experiment path.