Hello, just for the record - the 5.1 branch is end of life, you should upgrade to a newer supported stable branch. Are your errors only related to the MY_CUSTOM_FLAG variable injection? Does it work reliable if you build directly from source in your CI/CD environment, or fails at well? I would try to tackle this issue by the usual process, step by step trying to change different points in the environment to find the one that causes the problem.