The new Application Loadbalancer (ALB) from AWS stores it's access logs in a slightly different format to S3 than the classic ELB.
- logs are written every 5 minutes now
- some fields are added at the beginning of each line and some at the end
- logs are written as gzipped streams with the ending .gz
Source: https://atombrenner.blogspot.fr/2017/02/how-to-gunzip-aws-loadbalancer-logs.html
I'll see if I can write a pull request.