While similar, the issue you have with Steam Audio is not the same as the linked issues.
The problem you are seeing is a poorly implemented FMOD plugin, looking at the source code for the FMOD wrapper found on GitHub I can see the process callback is not informing FMOD how long to remain active when all inputs to the effect have gone idle.
Your best bet would be to log a bug with Valve or create an issue on their GitHub explaining your usage so they can fix the bug.