Sometimes SSL certificate problem

Approximateley every 20. build interrupts with the following error:

gitlab-ci-multi-runner 1.1.3 (a470667)
Using Shell executor...
Running on GITLAB-SRV-07...
Fetching changes...
HEAD is now at 0d44302 Merge branch 'fix-compression-rate' into 'master'
fatal: unable to access 'https://gitlab-ci-token:xxxxxx@domain.tld/group-namespace/repository.git/': SSL certificate problem: unable to get local issuer certificate

ERROR: Build failed: exit status 1

In this case I press "retry" and the build works as expected. But somethimes I get this error two or more times in sequence.

concurrent = 1

[[runners]]
  url = "https://domain.tld/ci"
  token = "xxxxxx"
  name = "GITLAB-SRV-07"
  executor = "shell"
  shell = "powershell"
  [runners.ssh]
  [runners.docker]
    image = ""
    privileged = false
  [runners.parallels]
    base_name = ""