I found this question while trying to solve the exact same issue. I am not sure if you have managed to solve this by now, but what I discovered is that the default value in the Helm chart for dags.gitSync.subPath is set to "tests/dags" so unless your DAG files are in that folder inside your repo the serialization process running on the scheduler pod never picks them up. They therefor never land up in your DB and the web frontend can't see them.

Setting this configuration parameter correctly for my repo structure solved my problem.