This environment is missing some function environment variable values.

### Before opening, please confirm:

- [X] I have checked the [custom domains troubleshooting guide](https://docs.aws.amazon.com/amplify/latest/userguide/custom-domain-troubleshoot-guide.html).
- [X] I have read the guide for [submitting bug reports](https://github.com/aws-amplify/amplify-hosting/blob/master/CONTRIBUTING.md).
- [X] I have done my best to include a minimal, self-contained set of instructions for consistently reproducing the issue.

### App Id

d2004l7njftm5k

### Region

eu-central-1

### Step

Backend Build

### Status

Build failed

### Issue or question

Hi,
Thank you in advance for your support.
We are working on a inherit project with Vue.JS / Nuxt, and when we try to start the build process in Amplify project, it seems to be missing a variable named S3_BUCKET which we are not aware of and not found in all other AWS services.
"This environment is missing some function environment variable values"

We know that seems intuitive, but already tried to remove this function in code and push to repo, and the same thing happens.
The repository is stored in CodeCommit, and uses some Lambda functions.

We tried to check all parameters in these services, but that one mentioned it's not present. Also, we reached out to the previous developer, and he was also unable to identify the issue, said it never happened.
Even when we try to redeploy the last successful build, it fails.

The question is: Is there a way to bypass this missing variable just to check if build will work; or maybe this is a recurring error that requires specific steps to rebuild project?
Does the error occur because of this function or because of the session identifier?

Let me know if you need more information.
We've been stuck with this error for a month. Appreciate any help.

### Error message


### Additional information

A curiosity: I don't know if this is normal, but most times when a new deploy happens, the message to reconnect repository appears. When I reconnect, and go back to the build screen it shows this error reported about environment variables missing.

No project files or tests are named. Start by tracing the Amplify backend build's Lambda environment-variable configuration for S3_BUCKET and reviewing the CodeCommit and redeployment setup; done means identifying the missing or stale reference and verifying a successful build or documented reproduction.

Written by the indexing model from the issue text.