Cool glad you found the error. 
RE: However, I tried to change the variables and in that case the deployment haven’t even started due to missing credentials.
Um 
The credentials you use locally on your machine with AWS_SECRET_KEY should be fine. Only need to remove the credentials from the .env files. Though you’ll have to update your app so that it doesn’t use those AWS Lambda reserved variables if they do. FWIW, I usually use an AWS profile.
Here’s another post where that person removed the AWS_ and updated his app. Error while deploying: AWS_ACCESS_KEY_ID reserved environment variable - Jets - BoltOps Community
Interesting, thought that I provided a safeguard check for reserved env variables in check reserved lambda variables and let user know by tongueroo · Pull Request #148 · rubyonjets/jets · GitHub Guessing you’re using Jets Afterburner mode and maybe the safeguard doesn’t check in that case. Anyway, will double check that later.