I don’t have a solution for you, sorry. The fact that it actually works for you sometimes suggests that it’s an issue with your build infrastructure not your Unity project or FMOD. I suspect it’s something to do with Unity running in Gitlab Runner and/or docker but, beyond that, I have no further suggestions.
I know other people are successfully using game-ci with FMOD but I’m not aware of any guides/tutorials and we certainly don’t have an official one ourselves.