We have recently experienced an issue caused by a combination of Timeline and FMOD.
Currently, if you’re in editor and try to use a FMOD Timeline track, FMOD Creates a Runtime Manager Instance so it can play the sound while you’re editing the Timeline Track.
Unfortunately, if you save and exit Unity, load up the same scene, and any Timeline FMOD Track, it now adds another Runtime Manager, and you can repeat the process and it will add more. This proceeds to cause issues if you loads scenes additevely or if you attempt to stop the Timeline Tracks due to them running on an untracked RuntimeManager instance.
We’ve managed to fix the issue by destroying all copies instead of only the instanced one before it enters play mode or it builds, but we’re not sure if this can cause some other problems down the line and it will be nice to see it fixed in case anyone else encounters it in a future release.
Hope this is enough information, we’re running 1.10.10 with Unity 2018.3.0f2.