Pipeline not running (Protected branches?)

Hello,

I have a pipeline running for merge requests which is running perfectly, until i encountered a merge request where the commit / source branch was master. so master → master. I noticed the source branch was protected. i then set it to unprotected, closed/re-opened the MR which then received new commits . still, the pipeline does not run. Manually running the pipeline shows the not so helpful error.

pre_parser_v1.1:
    image: php:8.1
    stage: deploy
    script: 
        - |
          ...
          ./pre_parser_1.sh
    rules:
        - if: $CI_PIPELINE_SOURCE == "merge_request_event"
        - if: $CI_PIPELINE_SOURCE == "web"
        - if: $CI_COMMIT_BRANCH == "master"
            when: manual

It works as expected for other merge requests. I feel i’ve tried everything, is it simply not possible for merge requests to be triggered if the source branch is “master” (even when unprotected?)

thanks for reading