Pushing docker containers to registry fails regularly

I have a script pushing docker containers to the registry and it regularly shows the same failure pattern:

The upload starts, most of the layers are already known and then the last layer’s upload will slow down and then eventually timeout. Then it will restart and restart…

The funny thing is that I’ve been doing this from several places without any problems but now we are in Berlin and the failures have started to happen consistently.
If I set a VPN (using Netherlands), the transfers complete properly.

While the transfers are failing, the connection here is working perfectly, I have a 100mb/s upload speed and even a network test while the upload is in timeout shows that everything is fine. I can even do torrenting with many open connections, etc while the upload to gitlab.com is failing.

I thought it could be my provider, so I did the same through 3G to see… timeouts as well.

There is something about uploading from the Berlin area.
Looks like gitlab’s tech support is paid only, although this is something I’m sure they’d could be interested to hear but I’m not sure how to communicate it to them. They are sitting behind cloudflare which could also be the source of the local problem.