See for example
https://travis-ci.org/jruby/jruby/jobs/248152331
full log:
https://s3.amazonaws.com/archive.travis-ci.org/jobs/248152331/log.txt?X-Amz-Expires=30&X-Amz-Date=20170629T111114Z&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAJRYRXRSVGNKPKO5A/20170629/us-east-1/s3/aws4_request&X-Amz-SignedHeaders=host&X-Amz-Signature=b46d90142afee2f6e48d3287a2e89f69a830aeed9f0a1309e381d81fe572a569

I cannot reproduce locally.
Maybe this is somewhat related to entropy?