Hey there 
As you can see my music systems contains out of 2 blocks. Left contains the complete song, right a minimal version. Everytime certain conditions turn true in Unity, the FMOD Labeled Parameter is switching btw the states “Driving” and “Standing”. In FMOD the transitions sounds smooth. In-Game, specially noticeable on the drums, there will be an overlapping sound. When the transition is done, everything sounds normal again. Although sometimes a track seems to stay delayed until another transition starts.
For me it sounds like a coding problem, but i don’t see what could be wrong there.
Also i had the issue of tracks staying delayed, when i was switching to the pause menu. Here some tracks should be muted. I fixed this by having a parameter for the pause menu with a volume automation which never goes to -endless dB.
Any ideas on this?
Kindest regards!