S3 output plugin through socks proxy

Im trying to use the s3 output plugin to share and backup logs,and this works as expected in out test environment. But in UAT and PROD environment I keep getting an "The error reported is: \n End of file reached" error.
The only difference between the environments is that internet access is allowed via SOCKS proxy in the more production like networks.

I've managed to exclude time synch and IAM policy problems, so the most likely problem is the proxy. It sounds like this is a problem reported by the underlying OS (which is Centos) but we're using the same OS and S# bucket in test, where it works. The only difference is the proxy..

Has anyone seen these problems and managed to solve them?
Any ideas where to search next?

Any help appreciated...

There is https://www.elastic.co/guide/en/logstash/current/plugins-outputs-s3.html#plugins-outputs-s3-proxy_uri, but I'm not really sure how it's set :frowning: