Can't push a specific docker image to container registry

I have a build script that is building 3 docker images, in parallel, and sending them to gitlab’s registry.

The images are quite small (< 200mb)

One of them keeps failing. Two of the images go through, one of them just hangs.

e7679424c8b3: Pushing [==================================================>] 24.15MB

and it will stay like that very long, until timeout.
the other two images don’t have that problem…

this happens:

  • across two networks (local in Germany, Netherlands with VPN)
  • on a 100mb upload connection
  • with fresh rebuild of the images
  • across reboots from the machine
  • when trying to upload it by itself

It will stay stuck like this, until timeout.

So it looks like there is something that the server doesn’t like about that image.
What could cause this?