Artifacts Download leads to 500 Whoops, something went wrong on our end

I’ve got gitlab-ce 13.12.15 (self-managed) and a project that produces artifacts. The artifacts are uploaded to the server with the message:

Uploading artifacts for successful job 00:01
Uploading artifacts...
Runtime platform                                    arch=amd64 os=linux pid=85324 revision=bd40e3da version=14.9.1
dist/: found 156 matching files and directories    
Uploading artifacts as "archive" to coordinator... 201  id=2845 responseStatus=201 token=ri9xux3W

This looks fine to me. But when I would like to do something with the artifact like for example “Browse” the Job artifacts within GitLab, I get the “500 Whoops, something went wrong on our end.” error message.

I can download the file and it has a size of 2MB. But I can’t open it. I get the message: “The folder cannot be opened. The zip folder is not guilty.”

Artifacts are configured as:

  artifacts:
    name: "$CI_JOB_NAME-$CI_JOB_STAGE-$CI_COMMIT_REF_NAME"
    expire_in: never
    paths:
      - dist/

dist/ has files and directories.

The GitLab-Runner is running in a docker container as shell executor. Git-Lab itself is also running in a docker container with ubuntu 16.04.

Now: Everything was fine last week. Then we got a problem with the certificate for GitLab. We changed to serve this by the firewall and pass it on to GitLab.

Any idea what the problem could be?

One more Point: I just noticed that the gitlab-runner is an older version then the one that comes with gitlab. So I upgraded it to version 15.9.1 But the error message is still the same:

Uploading artifacts for successful job 00:01
Uploading artifacts...
Runtime platform                                    arch=amd64 os=linux pid=95005 revision=d540b510 version=15.9.1
dist/: found 156 matching artifact files and directories 
Uploading artifacts as "archive" to coordinator... 201  id=2849 responseStatus=201 token=oenS5x22

And the artifact still has the same problem as well.