Rsync from inside container intermittently hangs

Hi,

I have docker the Docker Engine community 20.10.2 running on a CentOs 7.9.2009.
inside docker I have various containers (debian stretch/ debian buster/ alpine 3.12) all experiencing same issue:

I try to upload a large (nearly 1GB) file to Akamai via rsync.

this rsync command intermittently hangs. I run rsync with the --progress and watch it transfer. 12-14MB/s for multiple seconds - and then it suddenly stops. no further progress updates until, after 10 or 15 minutes it times out.
typically it successfully transfers 60 MB before it fails - sometimes multiple hundred MB.
sometimes it even succeeds - but I often need a dozen attempts to get the file through.

interestingly, the same command executed on the host system works perfectly fine each time.

as said, the issue happens only inside the docker container. so it somehow is related to docker.
it happens on various different OS images. so it doesn’t seem to be related to a specific image.
I have the latest docker version on a host os that’s on the latest update level (ok, I could update to CentOS 8.x).

any ideas? how could I further troubleshoot this?

Regards
sthones

I mentioned Akamai in my original question. the same happens when I rsync to a different target - so again, it’s also not related to the target system.