Test coverage parsing fails

I am trying to get gitlab code coverage parsing working. The server is a local instance of Gitlab 10.4.1-ee. The code coverage tool is lcov via a slightly modified version of this cmake file.

I've entered the regex into the CI Settings as well as in the gitlab ci file and see no output. From what I understand the code coverage will not even attempt to parse if this is not supplied. It did work on one job (out of hundreds) and never again (not sure why). I have supplied both the output and the regex as inputs into http://rubular.com and it seems to parse correctly. I've also fooled around with various iterations of including the single quotes or not or the slashes or not in the regex also to no avail. I can't see where we can get any debugging output or something to show that this step is actually performed.

The project's CI/CD Settings > Test coverage parsing entry:

\bOverall\D+(\d+[.]\d\%)

The job's relevant .gitlab-ci.yml

coverage:
  stage: build
  image: <redacted>:stable
  script:   
    - mkdir build
    - cd build
    - cmake -DCMAKE_BUILD_TYPE=Debug .. && make coverage
  coverage: '/(?m)\bOverall\D+(\d+[.]\d\%)/'
  artifacts:
    paths:
      - build/coverage/

The job's relevant output:

Overall coverage rate:
  lines......: 95.2% (749 of 787 lines)
  functions..: 96.5% (110 of 114 functions)
Open ./coverage/index.html in your browser to view the coverage report.
[100%] Built target coverage
Uploading artifacts...
build/coverage/: found 63 matching files           
Uploading artifacts to coordinator... ok            id=20671 responseStatus=201 Created token=kRnB--qX
Job succeeded